fix: exercises/udacity-c2-basic-server/package.json & exercises/udacity-c2-basic-server/package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-COOKIE-8163060

Author: snyk-bot

exercises/udacity-c2-basic-server/package-lock.json

@@ -33,7 +33,7 @@
     "typescript": "^3.5.3"
   },
   "dependencies": {
-    "express": "^4.20.0",
+    "express": "^4.21.1",
     "swagger-ui-express": "^4.1.4"
   }
 }