Lock down sass-rails gem to version 4.0.3

This to be able to run bundle outdated.
Update to RSpec 3

Read more about all changes at:
https://www.relishapp.com/rspec/rspec-rails/v/3-0/docs/changelog

To understand this upgrade read at:
https://www.relishapp.com/rspec/rspec-rails/docs/upgrade and
https://relishapp.com/rspec/docs/upgrade