Update community_engine.gemspec sass-rails version

Update dependencey on sass-rails from 4.0.0 to 4.0.2 per https://github.com/jhthorsen/mojolicious-plugin-bootstrap3/commit/8f8859a1da78b10321ec3cfea6f5a2099eda22a1. Attempting to fix https://github.com/bborn/communityengine/issues/216