Update specs to RSpec 3.0.0.beta2 syntax with Transpec

This conversion is done by Transpec 1.13.1 with the following command:
    transpec

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

* 1 conversion
    from: allow(obj).to receive(:message).and_return
      to: allow(obj).to receive(:message)