Update dependency clean-css to v5.3.1

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
clean-css	5.2.4 -> 5.3.1

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Release Notes

clean-css/clean-css

### [`v5.3.1`](https://togithub.com/clean-css/clean-css/blob/HEAD/History.md#​531--2022-07-13-httpsgithubcomclean-cssclean-csscomparev530v531) [Compare Source](https://togithub.com/clean-css/clean-css/compare/v5.3.0...v5.3.1) \================== - Fixed issue [#​1218](https://togithub.com/clean-css/clean-css/issues/1218) - double hyphen in at-rule breaks parsing. - Fixed issue [#​1220](https://togithub.com/clean-css/clean-css/issues/1220) - adds optimization for nth-\* rules. ### [`v5.3.0`](https://togithub.com/clean-css/clean-css/blob/HEAD/History.md#​530--2022-03-31-httpsgithubcomclean-cssclean-csscomparev523v530) [Compare Source](https://togithub.com/clean-css/clean-css/compare/v5.2.4...v5.3.0) \================== - Adds customizable value optimizers for variables. - Fixed issue [#​1159](https://togithub.com/clean-css/clean-css/issues/1159) - adds optimization for `nth-child` and `nth-of-type`. - Fixed issue [#​1181](https://togithub.com/clean-css/clean-css/issues/1181) - CSS level 4 color functions with spaces. - Fixed issue [#​1183](https://togithub.com/clean-css/clean-css/issues/1183) - fraction optimizer breaks `image-set`. - Fixed issue [#​1208](https://togithub.com/clean-css/clean-css/issues/1208) - handling generic family names. - Fixed issue [#​1210](https://togithub.com/clean-css/clean-css/issues/1210) - handling `file://` protocol.

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