Bump postcss from 8.2.13 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.13 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@8.2.13...8.4.31)

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

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

package.json

@@ -40,7 +40,7 @@
     "fs": "0.0.1-security",
     "jest": "^26.6.3",
     "node-fetch": "2.6.7",
-    "postcss": "^8.1.14",
+    "postcss": "^8.4.31",
     "prettier": "^2.2.1",
     "prettier-plugin-svelte": "^2.2.0",
     "rollup": "^2.3.4",