Update specs to RSpec 2.14.8 syntax

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

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

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

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

* 3 conversions
    from: stub('something')
      to: double('something')

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