fix: upgrade clean-css from 5.2.0 to 5.2.1

Snyk has created this PR to upgrade clean-css from 5.2.0 to 5.2.1.

See this package in npm:
https://www.npmjs.com/package/clean-css

See this project in Snyk:
https://app.snyk.io/org/johnmclear/project/d9a12bfb-7ccd-443f-9e22-f30d339cc8c5?utm_source=github&utm_medium=referral&page=upgrade-pr

src/package-lock.json

@@ -1271,9 +1271,9 @@
       "optional": true
     },
     "clean-css": {
-      "version": "5.2.0",
-      "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-5.2.0.tgz",
-      "integrity": "sha512-2639sWGa43EMmG7fn8mdVuBSs6HuWaSor+ZPoFWzenBc6oN+td8YhTfghWXZ25G1NiiSvz8bOFBS7PdSbTiqEA==",
+      "version": "5.2.1",
+      "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-5.2.1.tgz",
+      "integrity": "sha512-ooQCa1/70oRfVdUUGjKpbHuxgMgm8BsDT5EBqBGvPxMoRoGXf4PNx5mMnkjzJ9Ptx4vvmDdha0QVh86QtYIk1g==",
       "requires": {
         "source-map": "~0.6.0"
       }

src/package.json

@@ -32,7 +32,7 @@
   "dependencies": {
     "async": "^3.2.1",
     "channels": "0.0.4",
-    "clean-css": "^5.2.0",
+    "clean-css": "^5.2.1",
     "cookie-parser": "1.4.5",
     "cross-spawn": "^7.0.3",
     "ejs": "^3.1.6",