Update postcss version

Author: donhardman

addons/watercss/skel/app/client/package.json

@@ -28,7 +28,7 @@
     "node-sass": "^5.0.0",
     "oatmeal-cookie": "0.0.1",
     "optimize-css-assets-webpack-plugin": "^5.0.4",
-    "postcss": "8",
+    "postcss": ">=8.2.10",
     "postcss-100vh-fix": "^1.0.2",
     "postcss-assets": "^5.0.0",
     "postcss-at2x": "^5.0.0",