Use sass-rails 4.0.0

Finding sass-rails version is 4.0.0.rc1 when I create new app by `rails new` in Rails 4.1.0.beta1.
Rails 4.0.0 already use sass-rails version 4.0.0. 
So just change sass-rails version 4.0.0 instead of 4.0.0.rc1.