chore(deps): 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:production
  update-type: version-update:semver-major
...

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

package.json

@@ -25,7 +25,7 @@
         "debounce": "^1.2.1",
         "mini-css-extract-plugin": "^2.6.0",
         "mustache": "^4.0",
-        "postcss-loader": "^7.0.1",
+        "postcss-loader": "^8.1.0",
         "sass": "^1.51.0",
         "sass-loader": "^13.1.0",
         "vue": "^2.6.14",