fix: package.json & package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-POSTCSS-5926692

Author: snyk-bot

package-lock.json

@@ -87,7 +87,7 @@
     "remark-gemoji-to-emoji": "^1.1.0",
     "remark-parse": "^7.0.2",
     "remark-rehype": "^5.0.0",
-    "resolve-url-loader": "^4.0.0",
+    "resolve-url-loader": "^5.0.0",
     "revalidator": "^0.3.1",
     "rimraf": "^3.0.0",
     "rss-parser": "^3.12.0",