build(deps): bump clean-css from 5.2.4 to 5.3.0 in /src

Bumps [clean-css](https://github.com/clean-css/clean-css) from 5.2.4 to 5.3.0.
- [Release notes](https://github.com/clean-css/clean-css/releases)
- [Changelog](https://github.com/clean-css/clean-css/blob/master/History.md)
- [Commits](https://github.com/clean-css/clean-css/compare/v5.2.4...v5.3.0)

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

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

src/package.json

@@ -31,7 +31,7 @@
   ],
   "dependencies": {
     "async": "^3.2.2",
-    "clean-css": "^5.2.4",
+    "clean-css": "^5.3.0",
     "cookie-parser": "^1.4.6",
     "cross-spawn": "^7.0.3",
     "ejs": "^3.1.6",