fix(workflow_cli_release.groovy): prepend branch name with 'refs/'
fix(workflow_cli_release.groovy): prepend branch name with 'refs/'

As this is the precise `ref` value used in the github webhook
on the tag push event.  Hoping this will be the key to trigger this
job (previously, just using `tags/${RELEASE}` didn't seem to catch the event)

deis/jenkins-jobs