Bump postcss from 8.4.23 to 8.4.31 in /www

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.23 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.23...8.4.31)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
...

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

www/package.json

@@ -18,7 +18,7 @@
     "gulp-sass": "^5.1.0",
     "gulp-sourcemaps": "^3.0.0",
     "gulp-touch-fd": "^2.0.0",
-    "postcss": "^8.2.13",
+    "postcss": "^8.4.31",
     "sass": "^1.62.1",
     "socket.io": "^4.4.1",
     "string-width": "^5.1.0",