- Instead of using `to_f.phase`, just use `to_f.negative`?.
- This change works same for all cases except when number is "-0.0".
      -0.0.to_f.negative? => false
      -0.0.to_f.phase? => pi
- So -0.0 will be treated as positive from now onwards.
- So this change reverts changes from https://github.com/rails/rails/pull/6512.
- But it should be acceptable as we could not find any currency which
  supports negative zeros.