Update Ruby version.
Convert specs to RSpec 3.0.1 syntax with Transpec

This conversion is done by Transpec 2.2.4 with the following command:
    transpec -f

* 15 conversions
    from: obj.should
      to: expect(obj).to

* 9 conversions
    from: == expected
      to: eq(expected)

For more details: https://github.com/yujinakayama/transpec#supported-conversions