Log Message:
www/ruby-sass-rails: update to 6.0.0

Update ruby-sass-rails to 6.0.0.

6.0.0 (2019-09-04)

Breaking change

* Move the implementation to sassc-rails.

* This gem is now only just a wrapper around sassc-rails. For more
  information on how sassc differs from Ruby sass see
  https://github.com/sass/sassc-rails#libsass-compatibility-with-ruby-sass.