Update RSpec dependency.

I've updated the `rspec-rails` dependency and updated all the existing specs using [transpec](https://github.com/yujinakayama/transpec) @ 9d201bb44d1d07d7a002f089299bee49b58f5fe7.
I'm not a big fan of this `:type =>` setting, but transpec ads it by default. We can remove those and use the `infer_spec_type_from_file_location!`config.