Upgraded to RSpec 3.1 and more recent Cucumber.

This brings up the project to a bunch of newer gems, starting with RSpec 3.x. This actually makes the project buildable and runnable with current state of gems out there - a lot of them weren't locked in .gemspec and now mostly everything fails.
 
There're some minitest tests that I removed from examples/rails3_root/test/mailers/user_mailer_spec_test.rb that I think test deprecated behavior with hanging `must` and `it`, but I am not 100% sure.