minor cleanup w/ chases's feedback from CL 6665018.

http://codereview.chromium.org/6665018/

Review URL: http://codereview.chromium.org/6686060

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@78098 0039d316-1c4b-4281-b951-d872f2087c98

git_cl/git_cl.py

@@ -741,10 +741,10 @@ def RunHook(committing, upstream_branch, rietveld_server, tbr, may_prompt):
 
   root = RunCommand(['git', 'rev-parse', '--show-cdup']).strip()
   if not root:
-    root = "."
+    root = '.'
   absroot = os.path.abspath(root)
   if not root:
-    raise Exception("Could not get root directory.")
+    raise Exception('Could not get root directory.')
 
   # We use the sha1 of HEAD as a name of this change.
   name = RunCommand(['git', 'rev-parse', 'HEAD']).strip()