Bump postcss from 8.4.17 to 8.4.18

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.17 to 8.4.18.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.17...8.4.18)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

package.json

@@ -50,7 +50,7 @@
     "lato-font": "^3.0.0",
     "mini-css-extract-plugin": "^2.6.1",
     "node-sass": "^7.0.3",
-    "postcss": "^8.4.17",
+    "postcss": "^8.4.18",
     "postcss-loader": "^7.0.1",
     "postcss-scss": "^4.0.5",
     "sass": "^1.55.0",