Added Simplecov.

Previously, quoting an array fell back to `inspect`, which is ok for
strings, but not good for BigDecimals, for instance.

This reverts commit 067ce522.

This conversion is done by Transpec 2.2.5 with the following command:
    transpec

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

* 27 conversions
    from: obj.should_receive(:message)
      to: expect(obj).to receive(:message)

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

* 4 conversions
    from: obj.should_not
      to: expect(obj).not_to

* 4 conversions
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

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

changing to get rid of deprecation warnings