Bump autoprefixer from 10.4.20 to 10.4.21

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 10.4.20 to 10.4.21.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/main/CHANGELOG.md)
- [Commits](postcss/autoprefixer@10.4.20...10.4.21)

---
updated-dependencies:
- dependency-name: autoprefixer
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Diff for: package-lock.json

@@ -33,7 +33,7 @@
     "@material/tab-scroller": "^14.0.0",
     "@material/top-app-bar": "^14.0.0",
     "@material/typography": "^14.0.0",
-    "autoprefixer": "^10.4.20",
+    "autoprefixer": "^10.4.21",
     "babel-core": "^6.26.3",
     "babel-loader": "^10.0.0",
     "babel-preset-es2015": "^6.24.1",