Bump postcss-loader from 3.0.0 to 5.2.0

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 3.0.0 to 5.2.0.
- [Release notes](https://github.com/webpack-contrib/postcss-loader/releases)
- [Changelog](https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md)
- [Commits](webpack/postcss-loader@v3.0.0...v5.2.0)

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

Author: dependabot[bot]

package-lock.json

@@ -30,7 +30,7 @@
         "entities": "^2.1.0",
         "mini-css-extract-plugin": "^1.4.0",
         "npm-run-all": "^4.1.5",
-        "postcss-loader": "^3.0.0",
+        "postcss-loader": "^5.2.0",
         "react": "16.8.6",
         "react-dom": "16.13.0",
         "react-instantsearch-dom": "6.8.2",