Update dependency clean-css to v5

Author: renovate-bot

package.json

@@ -34,7 +34,7 @@
     "@11ty/eleventy-plugin-rss": "^1.0.7",
     "@tryghost/content-api": "^1.2.5",
     "@tryghost/helpers": "^1.1.6",
-    "clean-css": "^4.2.1",
+    "clean-css": "^5.0.0",
     "cross-env": "^7.0.0",
     "dotenv": "^8.0.0",
     "eleventy-plugin-lazyimages": "liamfiddler/eleventy-plugin-lazyimages",

yarn.lock

@@ -790,6 +790,13 @@ clean-css@^4.1.11, clean-css@^4.2.1:
   dependencies:
     source-map "~0.6.0"
 
+clean-css@^5.0.0:
+  version "5.1.0"
+  resolved "https://registry.yarnpkg.com/clean-css/-/clean-css-5.1.0.tgz#f3cc8ba900ab23b316e753330d15425149be36f1"
+  integrity sha512-98ALLW4NOhZpvUEoSc2dJO23xE4S4SXc4mLieCVFGo8DNLTFQ3gzi7msW1lqSYJeGZSF5r5+W3KF6cEnkILnFQ==
+  dependencies:
+    source-map "~0.6.0"
+
 cli-cursor@^3.1.0:
   version "3.1.0"
   resolved "https://registry.yarnpkg.com/cli-cursor/-/cli-cursor-3.1.0.tgz#264305a7ae490d1d03bf0c9ba7c925d1753af307"