Update clean-css to the latest version 🚀

[greenkeeper]

Version 4.0.1 of clean-css just got published.

Dependency	clean-css
Current Version	3.4.24
Type	devDependency

The version 4.0.1 is not covered by your current version range.

Without accepting this pull request your project will work just like it did before. There might be a bunch of new features, fixes and perf improvements that the maintainers worked on for you though.

I recommend you look into these changes and try to get onto the latest version of clean-css.
Given that you have a decent test suite, a passing build is a strong indicator that you can take advantage of these changes by merging the proposed change into your project. Otherwise this branch is a great starting point for you to work on the update.

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Commits

The new version differs by 314 commits (ahead by 314, behind by 87).

• d2563d8 Version 4.0.1.
• 9b50b3e See #872 - two additional cases.
• bb2e191 Fixes #872 - edge case in tokenization.
• 9fa4f55 Fixes #868 - accept absolute paths in input hash.
• f6c6d11 Fixes #867 - skips optimizing variable values.
• c1d6c5f Fixes #866 - edge case in inline flag handling.
• bab6108 See #858 - updates web interface for clean-css 4.
• b9cc7bf Version 4.0.0.
• c7c658b Updates acknowledgements section.
• 80e2f45 See #864 - adds better docs for optimization levels.
• 05e792d Re-enables protocol tests on Windows.
• d806651 Reworks Readme to be more readable.
• 2b5e3f3 See #846 - moves CLI to a separate repository.
• fdf123b Cleans up serializer code.
• 84b71ae Renames 'star' to 'asterisk'.

There are 250 commits in total. See the full diff.

Not sure how things should work exactly?

There is a collection of frequently asked questions and of course you may always ask my humans.

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Your Greenkeeper Bot 🌴

[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

[greenkeeper]

Version 4.0.2 just got published.

Update to this version instead 🚀

Commits

The new version differs by 2 commits .

• e7821b4 Version 4.0.2.
• 0b34e25 Fixes #874 - regression in at-rule tokenization.

See the full diff.