Updates rails to 4.1.0.rc2

@rcristal 

- [release notes][1]
- [release announcement][2]
- [deprecation of db:test:* tasks][3]
- Had to update `sass-rails` to 4.0.2 because of
an [issue with sprockets 2.12][4]

[1]: http://edgeguides.rubyonrails.org/4_1_release_notes.html
[2]: http://weblog.rubyonrails.org/2014/3/25/Rails-4-1-rc2/
[3]: https://github.com/rails/rails/pull/13528
[4]: https://github.com/sstephenson/sprockets/issues/540