Bump postcss from 8.4.18 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.18 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@8.4.18...8.4.31)

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

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

package.json

@@ -13,7 +13,7 @@
     "bootstrap-sass": "^3.4.3",
     "cross-env": "^7.0.3",
     "laravel-mix": "^6.0.49",
-    "postcss": "^8.4.18",
+    "postcss": "^8.4.31",
     "sass": "^1.55.0",
     "sass-loader": "^13.1.0",
     "vue-loader": "^15.9.7",