Fix git 1.6.1 vs 1.6.5 underscore key issue. (Hooks side.)

BUG=none
TEST=git cl upload sets watchlist extracc on rietveld
issues
Review URL: http://codereview.chromium.org/460125

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@34078 0039d316-1c4b-4281-b951-d872f2087c98

git_cl_hooks.py

@@ -59,7 +59,7 @@ def RunHooks(hook_name, upstream_branch):
     files = [f.LocalPath() for f in options.change.AffectedFiles()]
     watchers = watchlist.GetWatchersForPaths(files)
     Backquote(['git', 'config', '--add',
-               'rietveld.extra_cc', ','.join(watchers)])
+               'rietveld.extracc', ','.join(watchers)])
 
   # Run the presubmit checks.
   if presubmit_support.DoPresubmitChecks(options.change,