Support sass (3.3.13)

[Andrei Kaleshka]

To have worked compass 1.1 the gem requires update of sass:

Bundler could not find compatible versions for gem "sass":
  In Gemfile:
    sass-rails (~> 4.0.3) ruby depends on
      sass (~> 3.2.0) ruby

    compass (= 1.1.0.alpha.3) ruby depends on
      sass (3.3.13)

[Rafael Mendonça França]

Just use sass-rails 5