Use portable argument to `xargs`

OSX doesn't know what `--null` is.
Return to previous branch after deploying
Merge branch 'new-deploy-4' of github.com:jugglinmike/misoproject.com into jugglinmike-new-deploy-4
Abort deploy in presence of uncommitted changes
Merge branch 'new-deploy-4' of github.com:jugglinmike/misoproject.com into jugglinmike-new-deploy-4
Deploy site