fix for new rspec
Convert specs to RSpec 3.1.7 syntax with Transpec

This conversion is done by Transpec 3.0.1 with the following command:
    transpec

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

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

* 7 conversions
    from: lambda { }.should_not
      to: expect { }.not_to

* 1 conversion
    from: obj.should_not
      to: expect(obj).not_to

For more details: https://github.com/yujinakayama/transpec#supported-conversions
pass headers through from #encode to #guess without affecting them