Revert "specify python2 in shebang"

"/usr/bin/python2" does not exist on Mac OSX (see #2382), so fuck people who have
"python" symlinked to "python3"

This reverts commit e5ed07e2

plugins/git-prompt/gitstatus.py

-#!/usr/bin/env python2
+#!/usr/bin/env python
 # -*- coding: UTF-8 -*-
 from subprocess import Popen, PIPE
 import re