Bump postcss from 8.3.11 to 8.4.0 (#993)

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.11 to 8.4.0.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.3.11...8.4.0)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -63,7 +63,7 @@
     "passport-jwt": "^4.0.0",
     "passport-local": "^1.0.0",
     "path-exists": "^4.0.0",
-    "postcss": "^8.3.11",
+    "postcss": "^8.4.0",
     "rc": "1.2.8",
     "redux": "4.1.2",
     "request-promise": "^4.2.6",