Resolve deprecation warnings in configuration_spec
Convert specs to RSpec 3.0.0 syntax with Transpec

This conversion is done by Transpec 2.2.4 with the following command:
    transpec

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

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

* 68 conversions
    from: it { should ... }
      to: it { is_expected.to ... }

* 14 conversions
    from: it { should_not ... }
      to: it { is_expected.not_to ... }

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

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

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

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

* 1 conversion
    from: =~ /pattern/
      to: match(/pattern/)

* 1 conversion
    from: failure_message_for_should { }
      to: failure_message { }

* 1 conversion
    from: failure_message_for_should_not { }
      to: failure_message_when_negated { }

* 1 conversion
    from: obj.should_not_receive(:message)
      to: expect(obj).not_to receive(:message)

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