Using a branch containing the word 'head' always deploys HEAD from master

Happens because of this line: https://github.com/jbarnette/vlad-git/blob/master/lib/vlad/git.rb#L15
Gave us quite the headache before finding the cause. :)

Is 'head' a protected word for branches in vlad-git, or can this check be rewritten to be more specific and thus allowing branches with 'head' in it?
