Update dependency gulp-clean-css to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
gulp-clean-css	^3.10.0 -> ^4.0.0

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Release Notes

scniro/gulp-clean-css (gulp-clean-css)

### [`v4.3.0`](https://togithub.com/scniro/gulp-clean-css/releases/tag/4.3.0) [Compare Source](https://togithub.com/scniro/gulp-clean-css/compare/4.2.0...4.3.0) - [clean-css @​ v4.2.3](https://togithub.com/jakubpawlowicz/clean-css/releases/tag/v4.2.3) release ### [`v4.2.0`](https://togithub.com/scniro/gulp-clean-css/releases/tag/4.2.0) [Compare Source](https://togithub.com/scniro/gulp-clean-css/compare/4.1.1...4.2.0) [#​69](https://togithub.com/scniro/gulp-clean-css/issues/69) ### [`v4.1.1`](https://togithub.com/scniro/gulp-clean-css/releases/tag/4.1.1) [Compare Source](https://togithub.com/scniro/gulp-clean-css/compare/4.1.0...4.1.1) [#​52](https://togithub.com/scniro/gulp-clean-css/issues/52) ### [`v4.1.0`](https://togithub.com/scniro/gulp-clean-css/releases/tag/4.1.0) [Compare Source](https://togithub.com/scniro/gulp-clean-css/compare/4.0.0...4.1.0) [#​71](https://togithub.com/scniro/gulp-clean-css/issues/71) ### [`v4.0.0`](https://togithub.com/scniro/gulp-clean-css/releases/tag/4.0.0) [Compare Source](https://togithub.com/scniro/gulp-clean-css/compare/3.10.0...4.0.0) - Deprecate supported node versions 4 & 5 (end of life) - Address security vulnerability issues

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Configuration

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