Bump postcss-loader from 7.3.4 to 8.1.0

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 7.3.4 to 8.1.0.
- [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@v7.3.4...v8.1.0)

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

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

Author: dependabot[bot]

package-lock.json

@@ -32,7 +32,7 @@
     "html-minifier": "4.0.0",
     "mini-css-extract-plugin": "2.7.6",
     "postcss": "8.4.33",
-    "postcss-loader": "7.3.4",
+    "postcss-loader": "8.1.0",
     "pug": "3.0.2",
     "sass": "1.70.0",
     "sass-loader": "13.3.3",