chore: upgrade postcss version

Author: timlrx

package-lock.json

@@ -24,7 +24,7 @@
     "next-mdx-remote": "^3.0.1",
     "next-seo": "4.24.0",
     "next-themes": "^0.0.14",
-    "postcss": "^8.2.8",
+    "postcss": "^8.2.15",
     "preact": "^10.5.13",
     "react": "17.0.2",
     "react-dom": "17.0.2",