Bump postcss-loader from 7.3.3 to 8.0.0 (#136)

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 7.3.3 to 8.0.0.
- [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@v7.3.3...v8.0.0)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package-lock.json

@@ -16,7 +16,7 @@
     "copy-webpack-plugin": "^11.0.0",
     "css-loader": "^6.7.3",
     "mini-css-extract-plugin": "^2.7.2",
-    "postcss-loader": "^7.0.2",
+    "postcss-loader": "^8.0.0",
     "resolve-url-loader": "^5.0.0",
     "sass": "^1.57.1",
     "sass-loader": "^13.2.0",