Spec cleanup

I fixed a lot of deprecation warnings for the upcoming rspec 3 and Rails 4.1.

Since the `Gemfile` is not locked the development environment pulls in the latest version of all gems (adhering to the restrictions specified in `Gemfile` and `.gemspec` of course).

That means the development environment pulled in rspec 2.99 through `"rspec-rails", "~> 2.10"`, which produces a lot of warnings. Also the dummy application wasn't working with Rails 4.1.

I basically fixed all these warnings / errors since I want to add a new feature in the test helper (`MoneyRails::TestHelpers`). Will open another MR for that.