build(deps-dev): bump autoprefixer from 10.4.20 to 10.4.21 (#1865)

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-version: 10.4.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

package.json

@@ -90,7 +90,7 @@
     "@vuepress/plugin-register-components": "2.0.0-rc.44",
     "@vuepress/plugin-search": "2.0.0-rc.41",
     "@vuepress/theme-default": "2.0.0-rc.49",
-    "autoprefixer": "10.4.20",
+    "autoprefixer": "10.4.21",
     "browser-sync": "3.0.4",
     "cheerio": "1.0.0",
     "cssnano": "7.0.6",