Bump postcss from 8.4.19 to 8.4.20

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.19 to 8.4.20.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.19...8.4.20)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -31,7 +31,7 @@
     "imagemin-webpack-plugin": "^2.4.2",
     "mini-css-extract-plugin": "^2.7.1",
     "sass": "^1.56.2",
-    "postcss": "^8.4.19",
+    "postcss": "^8.4.20",
     "postcss-loader": "^7.0.2",
     "postcss-scss": "^4.0.6",
     "prettier": "^2.8.1",