Update gems & convert specs to RSpec 3.1.7 (transpec)

This conversion is done by Transpec 3.0.6 with the following command:
    transpec -f spec

* 28 conversions
    from: obj.should
      to: expect(obj).to

* 16 conversions
    from: == expected
      to: eq(expected)

* 14 conversions
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

* 11 conversions
    from: =~ /pattern/
      to: match(/pattern/)

* 2 conversions
    from: Klass.any_instance.stub(:message)
      to: allow_any_instance_of(Klass).to receive(:message)

* 1 conversion
    from: obj.stub(:message).and_return { value }
      to: obj.stub(:message) { value }

For more details: https://github.com/yujinakayama/transpec#supported-conversions