Update .gitignore to ignore git_cl_repo that was renamed in 61694.

TEST=none
BUG=none

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@61734 0039d316-1c4b-4281-b951-d872f2087c98

.gitignore

 *.pyc
-/git-cl-repo
+/git_cl_repo
 /tests/pymox
 /tests/_trial
 /python