Bump postcss from 8.4.5 to 8.4.31 in /front (#80)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.5 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@8.4.5...8.4.31)

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

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front/package.json

@@ -13,7 +13,7 @@
     "autoprefixer": "^10.4.0",
     "next": "^12.1.0",
     "papaparse": "^5.3.1",
-    "postcss": "^8.4.5",
+    "postcss": "^8.4.31",
     "react": "^17.0.2",
     "react-dom": "^17.0.2",
     "tailwindcss": "^3.0.5"