git_cl/gclient: use python2

Newer distros are defaulting /usr/bin/python to python3, so use python2
explicitly so we continue working.

Review URL: https://codereview.chromium.org/1437773002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@297535 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/git_cl.py b/git_cl.py
index c212300..8fa8a30 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2.7
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.