Convert Rspecs to v. 3 syntax

This conversion is done by Transpec 2.3.7 with the following command:
    transpec

* 281 conversions
    from: obj.should
      to: expect(obj).to

* 172 conversions
    from: == expected
      to: eq(expected)

* 136 conversions
    from: it { should_not ... }
      to: it { is_expected.not_to ... }

* 90 conversions
    from: it { should ... }
      to: it { is_expected.to ... }

* 22 conversions
    from: obj.should_not
      to: expect(obj).not_to

* 7 conversions
    from: === expected
      to: be === expected

* 7 conversions
    from: > expected
      to: be > expected

* 5 conversions
    from: < expected
      to: be < expected

* 4 conversions
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

* 3 conversions
    from: =~ /pattern/
      to: match(/pattern/)

For more details: https://github.com/yujinakayama/transpec#supported-conversions