Upgrade to rspec-rails 3.0.0.beta
Rails 4.0.0 tests depend on sass-rails 4.0.1

sass-rails 4.0.0 actually depends on Rails 4.1.0 beta, so we can't use
it.
Convert to RSpec expect syntax
Remove I18n.enforce_available_locales warning

The warning message was:

  [deprecated] I18n.enforce_available_locales will default to true in
  the future. If you really want to skip validation of your locale you
  can set I18n.enforce_available_locales = false to avoid this message.