git deploy pushes to given branch (default master)

Signed-off-by: David Varvel <dvarvel@pivotallabs.com>
Merge pull request #182 from vito/git-deploy-use-branch

git deploy pushes to given branch (default master)
Fixed the services function so that Drone can launch containers on
custom images.
Merge branch 'master' of github.com:xpepper/drone

Conflicts:
	README.md