Update to the latst grit

The latest grit includes a patch for performance improvements.

Gemfile

@@ -8,7 +8,7 @@ gem "devise", "~> 1.5"
 gem "stamp"
 gem "kaminari"
 gem "haml-rails"
-gem "grit", :git => "https://github.com/gitlabhq/grit.git", :ref => "9536f306645f2d6b1f993ae02d3a29893ba8881f"
+gem "grit", :git => "https://github.com/gitlabhq/grit.git", :ref => "7f35cb98ff17d534a07e3ce6ec3d580f67402837"
 gem "gitolite", :git => "https://github.com/gitlabhq/gitolite-client.git", :ref => "9b715ca8bab6529f6c92204a25f84d12f25a6eb0"
 gem "carrierwave"
 gem "six"