Bump postcss from 8.3.5 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.5 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.3.5...8.4.31)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -87,7 +87,7 @@
  "mkdirp": "0.5.1",
  "ncp": "2.0.0",
  "parallelshell": "1.2.0",
- "postcss": "8.3.5",
+ "postcss": "8.4.31",
  "postcss-loader": "6.1.0",
  "postcss-prefix-selector": "1.10.0",
  "process": "0.11.10",