Add .rb files to regex that excludes changing files

The blocklist for changing specific files in the editor is here:

https://github.com/gollum/gollum/blob/d00fefc89be0ab22ab862a51299120a55ccd9280/lib/gollum/app.rb#L222-L232

See https://github.com/gollum/gollum-lib/pull/464