Update dependency postcss-functions to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss-functions	^3 -> ^4.0.0

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Release Notes

andyjansson/postcss-functions (postcss-functions)

### [`v4.0.2`](https://togithub.com/andyjansson/postcss-functions/blob/HEAD/CHANGELOG.md#402---2020-11-08) [Compare Source](https://togithub.com/andyjansson/postcss-functions/compare/86ae864bc1e10da06d4816d42e4f6e6d3333caaf...6bf27f8f0a2174092fab268b8d086bdf39a1578b) - Update to PostCSS 8. - Remove `glob` option. ### [`v4.0.1`](https://togithub.com/andyjansson/postcss-functions/compare/e4d782288f43eda811723e9f9756aa4b0e42118d...86ae864bc1e10da06d4816d42e4f6e6d3333caaf) [Compare Source](https://togithub.com/andyjansson/postcss-functions/compare/e4d782288f43eda811723e9f9756aa4b0e42118d...86ae864bc1e10da06d4816d42e4f6e6d3333caaf) ### [`v4.0.0`](https://togithub.com/andyjansson/postcss-functions/compare/02ed7b05c85f9ec781dcebf567eb1cfee8f16991...e4d782288f43eda811723e9f9756aa4b0e42118d) [Compare Source](https://togithub.com/andyjansson/postcss-functions/compare/02ed7b05c85f9ec781dcebf567eb1cfee8f16991...e4d782288f43eda811723e9f9756aa4b0e42118d)

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