Bump rollup-plugin-postcss from 3.1.8 to 4.0.0

Bumps [rollup-plugin-postcss](https://github.com/egoist/rollup-plugin-postcss) from 3.1.8 to 4.0.0.
- [Release notes](https://github.com/egoist/rollup-plugin-postcss/releases)
- [Changelog](https://github.com/egoist/rollup-plugin-postcss/blob/master/CHANGELOG-OLD.md)
- [Commits](https://github.com/egoist/rollup-plugin-postcss/compare/v3.1.8...v4.0.0)

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

package.json

@@ -60,7 +60,7 @@
         "rollup-plugin-eslint": "^7.0.0",
         "rollup-plugin-json": "^4.0.0",
         "rollup-plugin-node-resolve": "^5.2.0",
-        "rollup-plugin-postcss": "^3.1.8",
+        "rollup-plugin-postcss": "^4.0.0",
         "rollup-plugin-replace": "^2.2.0",
         "rollup-plugin-size-snapshot": "^0.12.0",
         "rollup-plugin-svgo": "^1.1.0",