Fix README build example to work out of box.
Fix README build example to work out of box.

- secret_key was set to use the access_key env variable

sneal/packer,rickard-von-essen/packer,rnaveiras/packer,zhuzhih2017/packer,hashicorp/packer,tas50/packer,marc-ta/packer,mansunkuo/packer,routelastresort/packer,paulmey/packer,tsmolka/packer,pieter-lazzaro/packer,mkuzmin/packer,tb3088/packer,pieter-lazzaro/packer,p1-nico/packer,mitchellh/packer,pvandervelde/packer,taliesins/packer,dave2/packer,life360/packer,ricardclau/packer,timsutton/packer,boumenot/packer,smaato/packer,tsmolka/packer,monkeylittleinc/packer,hashicorp/packer,danschaffer/packer,p1-nico/packer,routelastresort/packer,threatstream/packer,jimmythedog/packer,mansunkuo/packer,danschaffer/packer,p1-nico/packer,taliesins/packer,samdunne/packer,mafrosis/packer,pvandervelde/packer,youhong316/packer,quantang/packer,yoctocloud/packer,mohae/packer,jimmythedog/packer,quantang/packer,youhong316/packer,mefellows/packer,grubernaut/packer,legal90/packer,zhuzhih2017/packer,monkeylittleinc/packer,vtolstov/packer,pvandervelde/packer,grange74/packer,boumenot/packer,mitchellh/packer,mkuzmin/packer,monkeylittleinc/packer,rickard-von-essen/packer,dayglojesus/packer,Akasurde/packer,KohlsTechnology/packer,youhong316/packer,bryson/packer,dayglojesus/packer,tas50/packer,pieter-lazzaro/packer,tsmolka/packer,legal90/packer,arizvisa/packer,vtolstov/packer,tas50/packer,mwhooker/packer,Akasurde/packer,dave2/packer,yoctocloud/packer,arizvisa/packer,mitchellh/packer,taliesins/packer,ChrisLundquist/packer,esemplare/packer,danschaffer/packer,mayflower/packer,pvandervelde/packer,samdunne/packer,Akasurde/packer,pieter-lazzaro/packer,mitchellh/packer,tb3088/packer,mohae/packer,pvandervelde/packer,c22/packer,hashicorp/packer,mayflower/packer,tb3088/packer,timsutton/packer,markpeek/packer,timsutton/packer,sean-/packer,monkeylittleinc/packer,mitchellh/packer,grange74/packer,tas50/packer,mwhooker/packer,tb3088/packer,KohlsTechnology/packer,sneal/packer,mafrosis/packer,mansunkuo/packer,youhong316/packer,paulmey/packer,rnaveiras/packer,marc-ta/packer,quantang/packer,mefellows/packer,pvanbuijtene/packer,youhong316/packer,pvanbuijtene/packer,sneal/packer,atlassian/packer,grange74/packer,sean-/packer,markpeek/packer,timsutton/packer,jen20/packer,grubernaut/packer,timsutton/packer,jimmythedog/packer,ChrisLundquist/packer,smaato/packer,atlassian/packer,grange74/packer,threatstream/packer,pvanbuijtene/packer,dayglojesus/packer,boumenot/packer,sean-/packer,c22/packer,bryson/packer,ricardclau/packer,KohlsTechnology/packer,mohae/packer,life360/packer,paulmey/packer,sean-/packer,mayflower/packer,pecigonzalo/packer,tsmolka/packer,ChrisLundquist/packer,dave2/packer,ChrisLundquist/packer,routelastresort/packer,threatstream/packer,jen20/packer,mohae/packer,c22/packer,pecigonzalo/packer,bryson/packer,paulmey/packer,KohlsTechnology/packer,marc-ta/packer,arizvisa/packer,rnaveiras/packer,tsmolka/packer,mkuzmin/packer,sneal/packer,arizvisa/packer,danschaffer/packer,pecigonzalo/packer,paulmey/packer,samdunne/packer,mkuzmin/packer,legal90/packer,taliesins/packer,jen20/packer,atlassian/packer,monkeylittleinc/packer,paulmey/packer,vtolstov/packer,taliesins/packer,tas50/packer,markpeek/packer,bryson/packer,ChrisLundquist/packer,legal90/packer,smaato/packer,c22/packer,mkuzmin/packer,ricardclau/packer,dayglojesus/packer,rickard-von-essen/packer,rnaveiras/packer,Akasurde/packer,ChrisLundquist/packer,bryson/packer,vtolstov/packer,arizvisa/packer,rickard-von-essen/packer,esemplare/packer,zhuzhih2017/packer,c22/packer,esemplare/packer,mefellows/packer,grubernaut/packer,pecigonzalo/packer,dave2/packer,zhuzhih2017/packer,markpeek/packer,pvanbuijtene/packer,jen20/packer,grubernaut/packer,routelastresort/packer,yoctocloud/packer,timsutton/packer,dayglojesus/packer,KohlsTechnology/packer,jimmythedog/packer,legal90/packer,routelastresort/packer,mwhooker/packer,quantang/packer,hashicorp/packer,yoctocloud/packer,mafrosis/packer,youhong316/packer,mayflower/packer,marc-ta/packer,mohae/packer,markpeek/packer,pvandervelde/packer,rnaveiras/packer,ricardclau/packer,jimmythedog/packer,atlassian/packer,life360/packer,life360/packer,sneal/packer,atlassian/packer,tb3088/packer,Akasurde/packer,smaato/packer,pieter-lazzaro/packer,esemplare/packer,mafrosis/packer,mwhooker/packer,smaato/packer,dave2/packer,mefellows/packer,samdunne/packer,mansunkuo/packer,markpeek/packer,mkuzmin/packer,rnaveiras/packer,mafrosis/packer,grange74/packer,life360/packer,p1-nico/packer,bryson/packer,tsmolka/packer,zhuzhih2017/packer,grubernaut/packer,mayflower/packer,smaato/packer,atlassian/packer,tb3088/packer,rickard-von-essen/packer,sean-/packer,sean-/packer,boumenot/packer,ricardclau/packer,dave2/packer,vtolstov/packer,c22/packer,boumenot/packer,KohlsTechnology/packer,pvanbuijtene/packer,yoctocloud/packer,p1-nico/packer,samdunne/packer,threatstream/packer,tas50/packer,jen20/packer,esemplare/packer,zhuzhih2017/packer,jen20/packer,pieter-lazzaro/packer,danschaffer/packer,mansunkuo/packer,ricardclau/packer,threatstream/packer,mwhooker/packer,p1-nico/packer,grubernaut/packer,taliesins/packer,quantang/packer,arizvisa/packer