[docs] Update contributing.md to reflect the change of the default branch.
[docs] Update contributing.md to reflect the change of the default branch.

nmalaguti/karma,kjbekkelund/karma,Sanjo/karma,youprofit/karma,Dignifiedquire/karma,fivetanley/karma,jeffjewiss/karma,brenoc/karma,bitwiseman/karma,behzad88/karma,viruschidai/karma,aiboy/karma,toranb/karma,sja/karma,kahwee/karma,pmq20/karma,remy/karma,jsdir/karma,dannycroft/karma,johan/karma,dmitriiabramov/karma,ernsheong/karma,pavelgj/testacular,gayancliyanage/karma,rgaskill/karma,SamuelMarks/karma,hppycoder/karma,IveWong/karma,oyiptong/karma,hleeldc/karma,fivetanley/karma,Sanjo/karma,Dignifiedquire/karma,wesleycho/karma,andersjanmyr/karma,Dignifiedquire/karma,hppycoder/karma,karma-runner/karma,vtsvang/karma,mpj/testacular,WickyNilliams/karma,buley/karma,switchfly/karma,pmq20/karma,david-garcia-nete/karma,marthinus-engelbrecht/karma,toranb/karma,Klaudit/karma,ashtuchkin/testacular,rageshkrishna/karma,Sanjo/karma,jankopriva/karma,skycocker/karma,garcimouche/karma,gfxmonk/karma,KidkArolis/karma,SamuelMarks/karma,patrickporto/karma,xiaoking/karma,MiCHiLU/testacular,clbond/karma,IveWong/karma,robdodson/karma,czchen/karma,mprobst/karma,xdissent/karma,skycocker/karma,mpj/testacular,bertrandgressier/karma,astorije/karma,andersjanmyr/karma,buley/karma,pavelgj/testacular,ijobling/karma,chrisirhc/karma,ashtuchkin/testacular,rhlass/karma,pmq20/karma,marthinus-engelbrecht/karma,Klaudit/karma,kahwee/karma,pedrotcaraujo/karma,david-garcia-nete/karma,tomkuk/karma,remy/karma,geddski/karma,aiboy/karma,eddiemonge/karma,thirtyseven/karma,IveWong/karma,unional/karma,Klaudit/karma,timols/karma,czchen/karma,shakyShane/karma,astorije/karma,jmendiara/karma,sylvain-hamel/karma,timols/karma,agrublev/karma,aiboy/karma,hexelon/karma,growlybear/karma,adamnation/karma,jfroom/karma,pmq20/karma,ryanflorence/testacular,mccalltd/karma,gdi2290/karma,taichi/testacular,xiaoking/karma,pedrosnk/karma,shirish87/karma,NimaVaziri/karma,yandex-lego/karma,tschaub/karma,powerkid/karma,lgalfaso/karma,peteryates/karma,KrekkieD/karma,IsaacChapman/karma,cironunes/karma,clbond/karma,amagee/karma,brianmhunt/karma,sym3tri/testacular,xiaoking/karma,ashaffer/karma,skycocker/karma,gayancliyanage/karma,johnjbarton/karma,zheller/karma,geddski/karma,harme199497/karma,clbond/karma,gayancliyanage/karma,hitesh97/karma,unional/karma,timebackzhou/karma,marthinus-engelbrecht/karma,nmalaguti/karma,patrickporto/karma,unional/karma,hindsightsoftware/karma,simudream/karma,unional/karma,davidmichaelkarr/karma,vtsvang/karma,markoa/karma,jeffjewiss/karma,brianmhunt/karma,chrisirhc/karma,maksimr/karma,marthinus-engelbrecht/karma,WickyNilliams/karma,maksimr/karma,dotfold/testacular,rgaskill/karma,timebackzhou/karma,tschaub/karma,tomkuk/karma,codedogfish/karma,revolunet/karma,pedrotcaraujo/karma,Grummle/karma,ck1125/karma,panrafal/karma,ahaurw01/testacular,hitesh97/karma,clbond/karma,karma-runner/karma,chrisirhc/karma,SamuelMarks/karma,Dignifiedquire/karma,powerkid/karma,wilkerlucio/karma,mprobst/karma,adamnation/karma,patrickporto/karma,jacopotarantino/karma,jeffjewiss/karma,dmitriiabramov/karma,karma-runner/karma,oyiptong/karma,adamnation/karma,johnjbarton/karma,wesleycho/karma,panrafal/karma,sylvain-hamel/karma,muffs/karma,jjoos/karma,Demeterr/karma,stevemao/karma,jfroom/karma,alextucker/testacular,harme199497/karma,panrafal/karma,powerkid/karma,simudream/karma,thirtyseven/karma,fredrikbonander/karma,rgaskill/karma,ernsheong/karma,simudream/karma,rhlass/karma,ernsheong/karma,aiboy/karma,jbdeboer/karma,jjoos/karma,alextucker/testacular,johnjbarton/karma,pedrosnk/karma,dotfold/testacular,zheller/karma,sylvain-hamel/karma,sublimino/karma,cironunes/karma,harme199497/karma,NimaVaziri/karma,harme199497/karma,thomasboyt/karma,Sanjo/karma,dannycroft/karma,KrekkieD/karma,drkibitz/karma,timebackzhou/karma,astorije/karma,stevemao/karma,alextucker/testacular,nmalaguti/karma,rhlass/karma,buley/karma,hleeldc/karma,johnjbarton/karma,r3mi/karma,lgalfaso/karma,sergeylukin/karma,stevemao/karma,david-garcia-nete/karma,codedogfish/karma,marcodejongh/karma,KrekkieD/karma,jamestalmage/karma,fredrikbonander/karma,growlybear/karma,skycocker/karma,behzad88/karma,sym3tri/testacular,jamestalmage/karma,swayf/karma,yandex-lego/karma,jamestalmage/karma,growlybear/karma,jmendiara/karma,Grummle/karma,thomasboyt/karma,rhlass/karma,brianmhunt/karma,behzad88/karma,timebackzhou/karma,lencioni/karma,astorije/karma,sja/karma,robdodson/karma,simudream/karma,kahwee/karma,hitesh97/karma,hitesh97/karma,matti/karma,ahaurw01/testacular,garcimouche/karma,jankopriva/karma,kahwee/karma,wilkerlucio/karma,lencioni/karma,ahaurw01/testacular,jjoos/karma,davidmichaelkarr/karma,swayf/karma,IsaacChapman/karma,xdissent/karma,vojtajina/karma,Basemm/karma,ryanflorence/testacular,xiaoking/karma,iammerrick/karma,markoa/karma,muffs/karma,tomkuk/karma,jsdir/karma,mccalltd/karma,machuga/karma,vtsvang/karma,hexelon/karma,rageshkrishna/karma,jacopotarantino/karma,bertrandgressier/karma,brenoc/karma,eddiemonge/karma,mpj/testacular,viruschidai/karma,sublimino/karma,ajoslin/karma,vtsvang/karma,powerkid/karma,KidkArolis/karma,chhsiao1981/testacular,machuga/karma,drkibitz/karma,johan/karma,bitwiseman/karma,Klaudit/karma,karma-runner/karma,wesleycho/karma,shirish87/karma,dmitriiabramov/karma,youprofit/karma,amagee/karma,IsaacChapman/karma,Demeterr/karma,yandex-lego/karma,makeusabrew/karma,jan-molak/karma,shakyShane/karma,mprobst/karma,jsdir/karma,MiCHiLU/testacular,switchfly/karma,gayancliyanage/karma,jamestalmage/karma,ijobling/karma,iammerrick/karma,tomkuk/karma,joakimkarlsson/karma,igorlima/karma,hindsightsoftware/karma,ashtuchkin/testacular,brianmhunt/karma,sergeylukin/karma,jan-molak/karma,KrekkieD/karma,chrisirhc/karma,igorlima/karma,oyiptong/karma,ijobling/karma,sym3tri/testacular,vojtajina/karma,revolunet/karma,jjoos/karma,nmalaguti/karma,r3mi/karma,rylnd/karma,rageshkrishna/karma,ajoslin/karma,codedogfish/karma,ck1125/karma,joakimkarlsson/karma,stevemao/karma,maksimr/karma,gdi2290/karma,MiCHiLU/testacular,IveWong/karma,bitwiseman/karma,buley/karma,shirish87/karma,matti/karma,marcodejongh/karma,kjbekkelund/karma,lencioni/karma,vojtajina/karma,ashaffer/karma,pedrosnk/karma,peteryates/karma,rylnd/karma,OniOni/karma,chhsiao1981/testacular,pedrotcaraujo/karma,agrublev/karma,gfxmonk/karma,wesleycho/karma,oyiptong/karma,Basemm/karma,patrickporto/karma,jbdeboer/karma,youprofit/karma,youprofit/karma,OniOni/karma,IsaacChapman/karma,codedogfish/karma,makeusabrew/karma,pedrotcaraujo/karma