Bug in zshprompt when no commits in repo

git rev-parse HEAD fails when there are no commits in a repo
and this script was very vocal about it. Removed that line from
the file. (NOTE: It is not used anywhere else to my knowledge.)
Merge pull request #1 from khwilson/patch-1

Bug in zshprompt when no commits in repo
Merge branch 'master' into knewton