We were using a fork to get the fix for
https://github.com/textmate/c.tmbundle/pull/24 before it was merged
upstream. Now it's been merged so we can go back to the upstream
repository.
This makes it so we don't have to redownload all the grammars every time
we build the grammars gem. It will also let us verify that grammars.yml
is accurate in the future by checking it against the submodules on disk.
script/bootstrap now updates the submodules.