Travis: auto rebase on master before running
Travis: auto rebase on master before running

It can happen that two PRs don't interfere with each other in the sense
that they hurt automatic rebasing, but still do not work together. The
prime example is PR1 changes the API of some function that PR2 uses. If
PR1 is merged, and PR2 is not rebased before merging, the error might
get unnoticed before the next build. Travis CI would have have told both
PR1 and PR2 are fine, but will complain (rather unnoticedly) that our
master does not compile.

This PR automatically rebases the PR on top of the current master,
before running the tests. If the automatic rebase fails, then this is
fine, because you will need to manually rebase again before merging,
anyway. The manual rebase, i.e. new push, will trigger Travis CI.

So, the main idea of this PR is that to can hit the "Restart Build"
button in Travis CI before hitting the merge button in Github.

ks156/RIOT,ros2/ros2_embedded_riot,stevenj/RIOT,Osblouf/RIOT,ros2/ros2_embedded_riot,beurdouche/RIOT,wentaoshang/RIOT,EmuxEvans/RIOT,syin2/RIOT,latsku/RIOT,ThanhVic/RIOT,RIOT-OS/RIOT,zhuoshuguo/RIOT,FrancescoErmini/RIOT,TobiasFredersdorf/RIOT,MohmadAyman/RIOT,nsol-nmsu/RIOT,smlng/RIOT,TobiasFredersdorf/RIOT,abkam07/RIOT,tfar/RIOT,tfar/RIOT,RBartz/RIOT,herrfz/RIOT,OlegHahm/RIOT,lebrush/RIOT,AnonMall/RIOT,lebrush/RIOT,josephnoir/RIOT,l3nko/RIOT,abp719/RIOT,katezilla/RIOT,daniel-k/RIOT,daniel-k/RIOT,rfswarm2/RIOT,sumanpanchal/RIOT,cladmi/RIOT,tdautc19841202/RIOT,kaleb-himes/RIOT,watr-li/RIOT,binarylemon/RIOT,ThanhVic/RIOT,bartfaizoltan/RIOT,Hyungsin/RIOT-OS,alex1818/RIOT,attdona/RIOT,emmanuelsearch/RIOT,EmuxEvans/RIOT,phiros/RIOT,jremmert-phytec-iot/RIOT,koenning/RIOT,LudwigKnuepfer/RIOT,PSHIVANI/Riot-Code,dailab/RIOT,avmelnikoff/RIOT,RBartz/RIOT,mziegert/RIOT,benoit-canet/RIOT,herrfz/RIOT-old,katezilla/RIOT,zhuoshuguo/RIOT,MohmadAyman/RIOT,RIOT-OS/RIOT,FrancescoErmini/RIOT,tdautc19841202/RIOT,kbumsik/RIOT,asanka-code/RIOT,stevenj/RIOT,zhuoshuguo/RIOT,l3nko/RIOT,roberthartung/RIOT,wentaoshang/RIOT,centurysys/RIOT,TobiasFredersdorf/RIOT,lebrush/RIOT,Lotterleben/RIOT,josephnoir/RIOT,adjih/RIOT,phiros/RIOT,backenklee/RIOT,Hyungsin/RIOT-OS,hamilton-mote/RIOT-OS,gebart/RIOT,herrfz/RIOT-old,toonst/RIOT,watr-li/RIOT,alex1818/RIOT,robixnai/RIOT,Josar/RIOT,jasonatran/RIOT,RubikonAlpha/RIOT,Ell-i/RIOT,ros2/ros2_embedded_riot,khhhh/RIOT,bartfaizoltan/RIOT,beurdouche/RIOT,rousselk/RIOT,thiagohd/RIOT,kbumsik/RIOT,RIOT-OS/RIOT,katezilla/RIOT,FrancescoErmini/RIOT,lazytech-org/RIOT,shady33/RIOT,dkm/RIOT,jferreir/RIOT,MonsterCode8000/RIOT,ntrtrung/RIOT,mtausig/RIOT,dkm/RIOT,attdona/RIOT,kaleb-himes/RIOT,roberthartung/RIOT,mziegert/RIOT,kushalsingh007/RIOT,OTAkeys/RIOT,kerneltask/RIOT,LudwigOrtmann/RIOT,Ell-i/RIOT,kb2ma/RIOT,khhhh/RIOT,thomaseichinger/RIOT,immesys/RiSyn,LudwigOrtmann/RIOT,A-Paul/RIOT,avmelnikoff/RIOT,neiljay/RIOT,authmillenon/RIOT,d00616/RIOT,AnonMall/RIOT,kb2ma/RIOT,josephnoir/RIOT,herrfz/RIOT-old,ntrtrung/RIOT,MohmadAyman/RIOT,herrfz/RIOT,Lotterleben/RIOT,thomaseichinger/RIOT,stevenj/RIOT,EmuxEvans/RIOT,MonsterCode8000/RIOT,DipSwitch/RIOT,attdona/RIOT,automote/RIOT,RBartz/RIOT,abkam07/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,Josar/RIOT,msolters/RIOT,shady33/RIOT,sgso/RIOT,altairpearl/RIOT,haoyangyu/RIOT,MarkXYang/RIOT,locicontrols/RIOT,yogo1212/RIOT,mtausig/RIOT,tfar/RIOT,stevenj/RIOT,BytesGalore/RIOT,jfischer-phytec-iot/RIOT,mfrey/RIOT,x3ro/RIOT,mziegert/RIOT,benoit-canet/RIOT,alignan/RIOT,msolters/RIOT,watr-li/RIOT,d00616/RIOT,shady33/RIOT,JensErdmann/RIOT,binarylemon/RIOT,zhuoshuguo/RIOT,jfischer-phytec-iot/RIOT,RIOT-OS/RIOT,brettswann/RIOT,ThanhVic/RIOT,MarkXYang/RIOT,avmelnikoff/RIOT,dhruvvyas90/RIOT,nsol-nmsu/RIOT,cladmi/RIOT,aeneby/RIOT,Yonezawa-T2/RIOT,rfuentess/RIOT,jasonatran/RIOT,jferreir/RIOT,gbarnett/RIOT,ks156/RIOT,dkm/RIOT,1blankz7/RIOT,basilfx/RIOT,TobiasFredersdorf/RIOT,adrianghc/RIOT,neumodisch/RIOT,tdautc19841202/RIOT,alex1818/RIOT,katezilla/RIOT,tfar/RIOT,MarkXYang/RIOT,thomaseichinger/RIOT,jhollister/RIOT,chris-wood/RIOT,plushvoxel/RIOT,Darredevil/RIOT,x3ro/RIOT,locicontrols/RIOT,basilfx/RIOT,BytesGalore/RIOT,rakendrathapa/RIOT,benoit-canet/RIOT,jremmert-phytec-iot/RIOT,rakendrathapa/RIOT,asanka-code/RIOT,centurysys/RIOT,openkosmosorg/RIOT,1blankz7/RIOT,hamilton-mote/RIOT-OS,dkm/RIOT,adjih/RIOT,herrfz/RIOT,LudwigKnuepfer/RIOT,rajma996/RIOT,rfuentess/RIOT,bartfaizoltan/RIOT,ros2/ros2_embedded_riot,adrianghc/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,gautric/RIOT,gebart/RIOT,sgso/RIOT,gbarnett/RIOT,malosek/RIOT,Yonezawa-T2/RIOT,kYc0o/RIOT,x3ro/RIOT,gbarnett/RIOT,plushvoxel/RIOT,jremmert-phytec-iot/RIOT,lazytech-org/RIOT,latsku/RIOT,syin2/RIOT,immesys/RiSyn,rajma996/RIOT,beurdouche/RIOT,sgso/RIOT,koenning/RIOT,adrianghc/RIOT,daniel-k/RIOT,biboc/RIOT,toonst/RIOT,beurdouche/RIOT,lebrush/RIOT,ros2/ros2_embedded_riot,abp719/RIOT,thiagohd/RIOT,gebart/RIOT,rfswarm2/RIOT,rousselk/RIOT,PSHIVANI/Riot-Code,watr-li/RIOT,alex1818/RIOT,jasonatran/RIOT,OTAkeys/RIOT,khhhh/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,benoit-canet/RIOT,Darredevil/RIOT,tdautc19841202/RIOT,malosek/RIOT,beurdouche/RIOT,malosek/RIOT,rajma996/RIOT,Osblouf/RIOT,A-Paul/RIOT,arvindpdmn/RIOT,brettswann/RIOT,aeneby/RIOT,daniel-k/RIOT,arvindpdmn/RIOT,jbeyerstedt/RIOT-OTA-update,watr-li/RIOT,patkan/RIOT,chris-wood/RIOT,yogo1212/RIOT,marcosalm/RIOT,altairpearl/RIOT,immesys/RiSyn,basilfx/RIOT,rajma996/RIOT,biboc/RIOT,marcosalm/RIOT,thomaseichinger/RIOT,kerneltask/RIOT,authmillenon/RIOT,kerneltask/RIOT,FrancescoErmini/RIOT,robixnai/RIOT,koenning/RIOT,emmanuelsearch/RIOT,basilfx/RIOT,patkan/RIOT,hamilton-mote/RIOT-OS,alex1818/RIOT,JensErdmann/RIOT,neiljay/RIOT,robixnai/RIOT,ThanhVic/RIOT,adjih/RIOT,abp719/RIOT,toonst/RIOT,l3nko/RIOT,binarylemon/RIOT,wentaoshang/RIOT,rfswarm/RIOT,phiros/RIOT,miri64/RIOT,automote/RIOT,FrancescoErmini/RIOT,phiros/RIOT,A-Paul/RIOT,Lotterleben/RIOT,brettswann/RIOT,changbiao/RIOT,Yonezawa-T2/RIOT,BytesGalore/RIOT,MarkXYang/RIOT,Osblouf/RIOT,koenning/RIOT,RubikonAlpha/RIOT,marcosalm/RIOT,malosek/RIOT,neiljay/RIOT,DipSwitch/RIOT,gebart/RIOT,LudwigOrtmann/RIOT,neumodisch/RIOT,rfuentess/RIOT,emmanuelsearch/RIOT,yogo1212/RIOT,malosek/RIOT,dhruvvyas90/RIOT,patkan/RIOT,roberthartung/RIOT,abp719/RIOT,toonst/RIOT,AnonMall/RIOT,ros2/ros2_embedded_riot,fnack/RIOT,LudwigKnuepfer/RIOT,JensErdmann/RIOT,msolters/RIOT,LudwigOrtmann/RIOT,herrfz/RIOT-old,thiagohd/RIOT,mziegert/RIOT,immesys/RiSyn,miri64/RIOT,backenklee/RIOT,kaspar030/RIOT,neumodisch/RIOT,binarylemon/RIOT,x3ro/RIOT,Lexandro92/RIOT-CoAP,mtausig/RIOT,Lexandro92/RIOT-CoAP,changbiao/RIOT,asanka-code/RIOT,haoyangyu/RIOT,chris-wood/RIOT,fnack/RIOT,Darredevil/RIOT,EmuxEvans/RIOT,ant9000/RIOT,kYc0o/RIOT,ThanhVic/RIOT,MonsterCode8000/RIOT,kbumsik/RIOT,alignan/RIOT,gautric/RIOT,altairpearl/RIOT,msolters/RIOT,backenklee/RIOT,attdona/RIOT,mfrey/RIOT,dkm/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,ximus/RIOT,syin2/RIOT,OTAkeys/RIOT,jbeyerstedt/RIOT-OTA-update,sgso/RIOT,Hyungsin/RIOT-OS,rakendrathapa/RIOT,dailab/RIOT,sumanpanchal/RIOT,rfswarm/RIOT,shady33/RIOT,rfswarm2/RIOT,DipSwitch/RIOT,Lexandro92/RIOT-CoAP,latsku/RIOT,sgso/RIOT,yogo1212/RIOT,ximus/RIOT,MonsterCode8000/RIOT,luciotorre/RIOT,dailab/RIOT,biboc/RIOT,l3nko/RIOT,malosek/RIOT,1blankz7/RIOT,altairpearl/RIOT,ant9000/RIOT,rousselk/RIOT,syin2/RIOT,robixnai/RIOT,locicontrols/RIOT,automote/RIOT,RBartz/RIOT,JensErdmann/RIOT,plushvoxel/RIOT,MohmadAyman/RIOT,kbumsik/RIOT,kaspar030/RIOT,PSHIVANI/Riot-Code,gbarnett/RIOT,luciotorre/RIOT,Yonezawa-T2/RIOT,Hyungsin/RIOT-OS,Darredevil/RIOT,lazytech-org/RIOT,EmuxEvans/RIOT,alignan/RIOT,backenklee/RIOT,herrfz/RIOT,khhhh/RIOT,jbeyerstedt/RIOT-OTA-update,A-Paul/RIOT,Lotterleben/RIOT,abp719/RIOT,altairpearl/RIOT,abkam07/RIOT,neumodisch/RIOT,RBartz/RIOT,robixnai/RIOT,d00616/RIOT,shady33/RIOT,EmuxEvans/RIOT,kbumsik/RIOT,automote/RIOT,roberthartung/RIOT,jferreir/RIOT,gebart/RIOT,chris-wood/RIOT,lebrush/RIOT,abp719/RIOT,d00616/RIOT,aeneby/RIOT,patkan/RIOT,kb2ma/RIOT,tdautc19841202/RIOT,zhuoshuguo/RIOT,neumodisch/RIOT,kerneltask/RIOT,ks156/RIOT,DipSwitch/RIOT,OTAkeys/RIOT,PSHIVANI/Riot-Code,herrfz/RIOT-old,khhhh/RIOT,A-Paul/RIOT,rfswarm/RIOT,locicontrols/RIOT,miri64/RIOT,abkam07/RIOT,kushalsingh007/RIOT,jhollister/RIOT,ant9000/RIOT,Osblouf/RIOT,daniel-k/RIOT,kerneltask/RIOT,OlegHahm/RIOT,asanka-code/RIOT,fnack/RIOT,josephnoir/RIOT,msolters/RIOT,mfrey/RIOT,ntrtrung/RIOT,mziegert/RIOT,Lexandro92/RIOT-CoAP,luciotorre/RIOT,rfswarm2/RIOT,rakendrathapa/RIOT,automote/RIOT,OlegHahm/RIOT,RubikonAlpha/RIOT,bartfaizoltan/RIOT,phiros/RIOT,locicontrols/RIOT,changbiao/RIOT,dhruvvyas90/RIOT,emmanuelsearch/RIOT,MonsterCode8000/RIOT,stevenj/RIOT,kYc0o/RIOT,Darredevil/RIOT,altairpearl/RIOT,AnonMall/RIOT,Osblouf/RIOT,rfswarm/RIOT,patkan/RIOT,immesys/RiSyn,hamilton-mote/RIOT-OS,ant9000/RIOT,basilfx/RIOT,wentaoshang/RIOT,AnonMall/RIOT,authmillenon/RIOT,haoyangyu/RIOT,attdona/RIOT,authmillenon/RIOT,latsku/RIOT,gautric/RIOT,jferreir/RIOT,emmanuelsearch/RIOT,mziegert/RIOT,kaleb-himes/RIOT,MarkXYang/RIOT,RubikonAlpha/RIOT,rajma996/RIOT,plushvoxel/RIOT,yogo1212/RIOT,ximus/RIOT,LudwigOrtmann/RIOT,Lotterleben/RIOT,Lexandro92/RIOT-CoAP,luciotorre/RIOT,smlng/RIOT,mtausig/RIOT,shady33/RIOT,changbiao/RIOT,thiagohd/RIOT,authmillenon/RIOT,rousselk/RIOT,patkan/RIOT,lazytech-org/RIOT,smlng/RIOT,ks156/RIOT,RIOT-OS/RIOT,1blankz7/RIOT,luciotorre/RIOT,neiljay/RIOT,AnonMall/RIOT,msolters/RIOT,herrfz/RIOT,openkosmosorg/RIOT,Josar/RIOT,kaleb-himes/RIOT,neumodisch/RIOT,l3nko/RIOT,chris-wood/RIOT,brettswann/RIOT,kaleb-himes/RIOT,centurysys/RIOT,jferreir/RIOT,cladmi/RIOT,ntrtrung/RIOT,jasonatran/RIOT,openkosmosorg/RIOT,adjih/RIOT,openkosmosorg/RIOT,kYc0o/RIOT,katezilla/RIOT,MohmadAyman/RIOT,l3nko/RIOT,rakendrathapa/RIOT,thomaseichinger/RIOT,rfswarm2/RIOT,x3ro/RIOT,chris-wood/RIOT,MonsterCode8000/RIOT,PSHIVANI/Riot-Code,OTAkeys/RIOT,gautric/RIOT,rfswarm2/RIOT,robixnai/RIOT,immesys/RiSyn,alignan/RIOT,rfuentess/RIOT,cladmi/RIOT,jferreir/RIOT,fnack/RIOT,josephnoir/RIOT,hamilton-mote/RIOT-OS,benoit-canet/RIOT,jhollister/RIOT,kYc0o/RIOT,alex1818/RIOT,adrianghc/RIOT,JensErdmann/RIOT,kushalsingh007/RIOT,gbarnett/RIOT,rousselk/RIOT,jremmert-phytec-iot/RIOT,jhollister/RIOT,kaspar030/RIOT,herrfz/RIOT,dhruvvyas90/RIOT,fnack/RIOT,kb2ma/RIOT,LudwigKnuepfer/RIOT,rfswarm/RIOT,attdona/RIOT,mtausig/RIOT,ThanhVic/RIOT,bartfaizoltan/RIOT,biboc/RIOT,jbeyerstedt/RIOT-OTA-update,tfar/RIOT,mfrey/RIOT,arvindpdmn/RIOT,MarkXYang/RIOT,sumanpanchal/RIOT,RubikonAlpha/RIOT,RubikonAlpha/RIOT,Lotterleben/RIOT,asanka-code/RIOT,centurysys/RIOT,avmelnikoff/RIOT,kushalsingh007/RIOT,emmanuelsearch/RIOT,ximus/RIOT,thiagohd/RIOT,latsku/RIOT,roberthartung/RIOT,abkam07/RIOT,rfswarm/RIOT,haoyangyu/RIOT,Hyungsin/RIOT-OS,alignan/RIOT,avmelnikoff/RIOT,changbiao/RIOT,binarylemon/RIOT,jasonatran/RIOT,smlng/RIOT,centurysys/RIOT,gbarnett/RIOT,stevenj/RIOT,tdautc19841202/RIOT,syin2/RIOT,PSHIVANI/Riot-Code,Lotterleben/RIOT,jbeyerstedt/RIOT-OTA-update,haoyangyu/RIOT,bartfaizoltan/RIOT,adrianghc/RIOT,smlng/RIOT,arvindpdmn/RIOT,Lexandro92/RIOT-CoAP,fnack/RIOT,RBartz/RIOT,brettswann/RIOT,locicontrols/RIOT,abkam07/RIOT,TobiasFredersdorf/RIOT,arvindpdmn/RIOT,d00616/RIOT,Ell-i/RIOT,Josar/RIOT,authmillenon/RIOT,d00616/RIOT,lebrush/RIOT,ntrtrung/RIOT,wentaoshang/RIOT,nsol-nmsu/RIOT,binarylemon/RIOT,dailab/RIOT,marcosalm/RIOT,ros2/ros2_embedded_riot,phiros/RIOT,jremmert-phytec-iot/RIOT,neiljay/RIOT,khhhh/RIOT,benoit-canet/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,openkosmosorg/RIOT,kb2ma/RIOT,jhollister/RIOT,rousselk/RIOT,dhruvvyas90/RIOT,lazytech-org/RIOT,sumanpanchal/RIOT,nsol-nmsu/RIOT,jhollister/RIOT,kushalsingh007/RIOT,koenning/RIOT,brettswann/RIOT,JensErdmann/RIOT,aeneby/RIOT,jfischer-phytec-iot/RIOT,Yonezawa-T2/RIOT,toonst/RIOT,ant9000/RIOT,asanka-code/RIOT,sumanpanchal/RIOT,Darredevil/RIOT,ks156/RIOT,rfuentess/RIOT,yogo1212/RIOT,openkosmosorg/RIOT,miri64/RIOT,dhruvvyas90/RIOT,Ell-i/RIOT,arvindpdmn/RIOT,centurysys/RIOT,biboc/RIOT,cladmi/RIOT,LudwigOrtmann/RIOT,plushvoxel/RIOT,jfischer-phytec-iot/RIOT,mfrey/RIOT,marcosalm/RIOT,DipSwitch/RIOT,zhuoshuguo/RIOT,daniel-k/RIOT,kaspar030/RIOT,Osblouf/RIOT,miri64/RIOT,1blankz7/RIOT,Josar/RIOT,haoyangyu/RIOT,BytesGalore/RIOT,ximus/RIOT,backenklee/RIOT,latsku/RIOT,FrancescoErmini/RIOT,wentaoshang/RIOT,sumanpanchal/RIOT,1blankz7/RIOT,luciotorre/RIOT,automote/RIOT,watr-li/RIOT,DipSwitch/RIOT,OlegHahm/RIOT,Ell-i/RIOT,locicontrols/RIOT,kaspar030/RIOT,ntrtrung/RIOT,kushalsingh007/RIOT,MohmadAyman/RIOT,changbiao/RIOT,ximus/RIOT,jfischer-phytec-iot/RIOT,nsol-nmsu/RIOT,BytesGalore/RIOT,koenning/RIOT,LudwigKnuepfer/RIOT,OlegHahm/RIOT,sgso/RIOT,rakendrathapa/RIOT,adjih/RIOT,gautric/RIOT,marcosalm/RIOT,jremmert-phytec-iot/RIOT,aeneby/RIOT,dailab/RIOT,rajma996/RIOT,Yonezawa-T2/RIOT,thiagohd/RIOT