Convert specs to RSpec 3.0.1 syntax with Transpec

This conversion is done by Transpec 2.3.1 with the following command:
    transpec

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

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

* 13 conversions
    from: obj.stub(:message => value)
      to: allow(obj).to receive_messages(:message => value)

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

* 3 conversions
    from: lambda { }.should
      to: expect { }.to

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

* 1 conversion
    from: lambda { }.should_not
      to: expect { }.not_to

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

For more details: https://github.com/yujinakayama/transpec#supported-conversions
Enforce rspec 3
Chenged main ruby-version to 2.1.2
Updated ruby versions used by travis