Fix deleting a file with spaces in its name on the git side

This is based on a bug report for felipe's git-remote-hg
and subsequent fix due to Peter van Zetten:
  https://github.com/felipec/git/issues/19
  https://github.com/felipec/git/pull/20
--set-upstream not --set_upstream!
Merge pull request #53 from xentac/typo

--set-upstream not --set_upstream!