Bump postcss and @vue/cli-service

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependency [@vue/cli-service](https://github.com/vuejs/vue-cli/tree/HEAD/packages/@vue/cli-service). These dependencies need to be updated together.


Updates `postcss` from 8.4.24 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.24...8.4.31)

Updates `@vue/cli-service` from 4.5.19 to 5.0.8
- [Release notes](https://github.com/vuejs/vue-cli/releases)
- [Changelog](https://github.com/vuejs/vue-cli/blob/dev/CHANGELOG.md)
- [Commits](https://github.com/vuejs/vue-cli/commits/v5.0.8/packages/@vue/cli-service)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: "@vue/cli-service"
  dependency-type: direct:development
...

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

package.json

@@ -25,7 +25,7 @@
     "@vue/cli-plugin-babel": "~4.5.0",
     "@vue/cli-plugin-router": "~4.5.0",
     "@vue/cli-plugin-vuex": "~4.5.0",
-    "@vue/cli-service": "~4.5.0",
+    "@vue/cli-service": "~5.0.8",
     "vue-template-compiler": "^2.6.11"
   }
 }