Bump cerdic/css-tidy from 1.5.6 to 1.5.7

Bumps [cerdic/css-tidy](https://github.com/Cerdic/CSSTidy) from 1.5.6 to 1.5.7.
- [Release notes](https://github.com/Cerdic/CSSTidy/releases)
- [Changelog](https://github.com/Cerdic/CSSTidy/blob/master/NEWS)
- [Commits](https://github.com/Cerdic/CSSTidy/compare/v1.5.6...v1.5.7

)

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