Change 'sass-rails' dev dependency to 'sassc-rails'

[storhet]

Any plans on doing this change? Since the sass-rails gem is deprecated and just a wrapper around sassc-rails.
For now it causes some problems when you try to start the server if there's no sass-rails gem present in your project Gemfile. The problematic file is /lib/spree_multi_domain.rb and on line#3 it fails with 'require': cannot load such file -- sass/rails (LoadError) (which makes sense :) )