Push cms beta version to 3.0b4.dev5

See https://github.com/divio/django-cms/commit/042f4953f6d2db66fd15e4cb748ab4b279f57947

It would be nice to have the latest 'dev' beta, as develop will become unusable when https://github.com/divio/django-cms/pull/2581 is going to be merged.