Merge remote-tracking branch 'upstream/master' into mh-merge-upstream
Merge pull request #1 from expa/mh-merge-upstream

merge from upstream
Merge pull request #2 from progrium/master

merge from upstream
Merge pull request #3 from progrium/master

merge from upstream v0.3.2
use DOKKU_IMAGE (i.e. progrium/buildstep)
Merge pull request #781 from expa/master

use DOKKU_IMAGE (i.e. progrium/buildstep)