devel/ruby-regexp_parser: update to 1.8.0

Update ruby-regexp_parser package to 1.8.0.

### [1.8.0] - 2020-09-20 - [Janosch Müller](mailto:janosch84@gmail.com)

### Changed

- dropped support for running on Ruby 1.9.x

### Added

- regexp flags can now be passed when parsing a `String` as regexp body
  * see the [README](/README.md#usage) for details
  * thanks to [Owen Stephens](https://github.com/owst)
- bare occurrences of `\g` and `\k` are now allowed and scanned as literal escapes
  * matches Onigmo behavior
  * thanks for the report to [Marc-André Lafortune](https://github.com/marcandre)

### Fixed

- fixed parsing comments without preceding space or trailing newline in x-mode
  * thanks to [Owen Stephens](https://github.com/owst)

(taca)