Bump @fullhuman/postcss-purgecss from 5.0.0 to 6.0.0

Bumps [@fullhuman/postcss-purgecss](https://github.com/FullHuman/purgecss) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/FullHuman/purgecss/releases)
- [Changelog](https://github.com/FullHuman/purgecss/blob/main/CHANGELOG.md)
- [Commits](FullHuman/purgecss@v5.0.0...v6.0.0)

---
updated-dependencies:
- dependency-name: "@fullhuman/postcss-purgecss"
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

package.json

@@ -32,7 +32,7 @@
     "test": "npm-run-all lint-css && npm run lint-html && npm run lint-js && npx hugo"
   },
   "devDependencies": {
-    "@fullhuman/postcss-purgecss": "5.0.0",
+    "@fullhuman/postcss-purgecss": "6.0.0",
     "@trimbleinc/modus-bootstrap": "1.6.3",
     "autoprefixer": "10.4.19",
     "clipboard": "2.0.11",