fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-BODYPARSER-7926860
- https://snyk.io/vuln/SNYK-JS-EXPRESS-7926867
- https://snyk.io/vuln/SNYK-JS-SEND-7926862
- https://snyk.io/vuln/SNYK-JS-SERVESTATIC-7926865

package.json

@@ -15,7 +15,7 @@
   "dependencies": {
     "axios": "^1.7.4",
     "cors": "^2.8.4",
-    "express": "^4.19.2",
+    "express": "^4.21.0",
     "express-slow-down": "^1.4.0",
     "fork-awesome": "^1.2.0",
     "fs-readfile-promise": "^3.0.0",