Bump postcss from 7.0.4 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.4 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@7.0.4...8.4.31)

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

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

package.json

@@ -82,7 +82,7 @@
     "optimize-css-assets-webpack-plugin": "5.0.1",
     "ora": "3.0.0",
     "pdf-image": "2.0.0",
-    "postcss": "7.0.4",
+    "postcss": "8.4.31",
     "postcss-cssnext": "3.1.0",
     "puppeteer": "1.8.0",
     "rename": "1.0.4",