Bump postcss-loader from 7.3.0 to 8.1.1

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 7.3.0 to 8.1.1.
- [Release notes](https://github.com/webpack-contrib/postcss-loader/releases)
- [Changelog](https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/postcss-loader@v7.3.0...v8.1.1)

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

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

package.json

@@ -75,7 +75,7 @@
         "less": "^4.1.3",
         "less-loader": "^11.1.0",
         "mini-css-extract-plugin": "^2.7.5",
-        "postcss-loader": "^7.3.0",
+        "postcss-loader": "^8.1.1",
         "prettier": "^2.8.8",
         "pretty-quick": "^3.1.3",
         "raw-loader": "^4.0.1",