don't blow up if branch isn't specified

we don't have a default branch specified, so the deployment_name
function blows up when it checks for the existence of the `branch`
variable. used fetch to fix that.
Merge branch 'do_not_blow_up_without_branch' of https://github.com/spikegrobstein/hipchat-rb into spikegrobstein-do_not_blow_up_without_branch