Bump postcss from 8.3.0 to 8.3.1

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.0 to 8.3.1.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.3.0...8.3.1)

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

package.json

@@ -60,7 +60,7 @@
     "jest": "^26.6.3",
     "mini-css-extract-plugin": "^1.6.0",
     "optimize-css-assets-webpack-plugin": "^6.0.0",
-    "postcss": "^8.3.0",
+    "postcss": "^8.3.1",
     "postcss-loader": "^5.3.0",
     "prettier": "^2.3.1",
     "prettier-webpack-plugin": "^1.2.0",