Also update the PRESUBMIT check to exclude git_cl/.

BUG=none
TEST=git-cl hooks run
TBR=maruel@chromium.org
Review URL: http://codereview.chromium.org/5998008

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@70108 0039d316-1c4b-4281-b951-d872f2087c98