Update dependency clean-css-cli to v5.2.1

Created by: renovate[bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
clean-css-cli	5.2.0 -> 5.2.1

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Release Notes

jakubpawlowicz/clean-css-cli

v5.2.1

Compare Source

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• Bumps clean-css dependency to 5.1.1.

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