Bump postcss from 8.1.4 to 8.1.6 (#32113)

Bumps [postcss](https://github.com/postcss/postcss) from 8.1.4 to 8.1.6.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.1.4...8.1.6)

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package.json

@@ -126,7 +126,7 @@
     "nodemon": "^2.0.6",
     "npm-run-all": "^4.1.5",
     "popper.js": "^1.16.1",
-    "postcss": "^8.1.4",
+    "postcss": "^8.1.6",
     "postcss-cli": "^8.2.0",
     "rollup": "^2.33.1",
     "rollup-plugin-istanbul": "^2.0.1",