Bump postcss from 8.4.30 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.30 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@8.4.30...8.4.31)

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

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

package.json

@@ -38,7 +38,7 @@
     "gulp-sourcemaps": "^3.0.0",
     "hint": "^7.1.3",
     "npm-check-updates": "^16.7.4",
-    "postcss": "^8.4.21",
+    "postcss": "^8.4.31",
     "postcss-calc": "^8.2.4",
     "postcss-colormin": "^5.3.0",
     "postcss-discard-empty": "^5.1.1",