Bump sass-rails from 5.1.0 to 6.0.0

Bumps sass-rails from 5.1.0 to 6.0.0.

Release notes

Sourced from sass-rails's releases.

6.0.0

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.

Commits

• a77240c Prepare to 6.0.0
• 8dbe4dc Bump version to 6.0.0.beta3
• 830a8ec Bump minimum version of sassc-rails
• ff54c20 Fix open-ended dependency
• ebe9ef7 Bump version to v6.0.0.beta2
• 409d871 Merge pull request #424 from rails/sassc-rails
• d809900 Recomend to use SassC::Rails::Importer to users requiring sass/rails/importer
• 706526d Make sass-rails an wrapper for sassc-rails to allow a smooth upgrade path
• ac38f1e Merge pull request #423 from gregmolnar/master
• d61b999 remove gemnasium badge from readme
• Additional commits viewable in compare view