Update dependency clean-css to v5.3.1

[renovate]

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

Compare Source

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• Fixed issue #​1218 - double hyphen in at-rule breaks parsing.
• Fixed issue #​1220 - adds optimization for nth-* rules.

v5.3.0

Compare Source

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• Adds customizable value optimizers for variables.
• Fixed issue #​1159 - adds optimization for nth-child and nth-of-type.
• Fixed issue #​1181 - CSS level 4 color functions with spaces.
• Fixed issue #​1183 - fraction optimizer breaks image-set.
• Fixed issue #​1208 - handling generic family names.
• Fixed issue #​1210 - handling file:// protocol.

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