Fix precompile issue in ckeditor.

Ckeditor has some invalid CSS that is causing sprockets to raise an invalid css issue when precompiling assets in a rails app.

I went ahead and applied the fix that was made in the ckeditor repository to the version included with rich.

Here is the commit that fixed the issue in the ckeditor repository:

https://github.com/galetahub/ckeditor/commit/889d05904da4a8c30d8b21e28af12ece76d157ca