Updates clean-css dependency to version 5.3.0.

Author: jakubpawlowicz

package-lock.json

@@ -35,7 +35,7 @@
   "homepage": "https://github.com/clean-css/clean-css-cli#readme",
   "dependencies": {
     "chokidar": "^3.5.2",
-    "clean-css": "^5.2.4",
+    "clean-css": "^5.3.0",
     "commander": "7.x",
     "glob": "^7.1.6"
   },