Update dependency clean-css-cli to v5.1.0

Created by: renovate[bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
clean-css-cli	5.0.1 -> 5.1.0

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Release Notes

jakubpawlowicz/clean-css-cli

v5.1.0

Compare Source

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• Fixed issue #​51 - excluding files via glob negated pattern.

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