fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:validator:20180218

Latest report for freecodecamp/freecodecamp:
https://snyk.io/test/github/freecodecamp/freecodecamp

package.json

@@ -66,7 +66,7 @@
     "express-flash": "~0.0.2",
     "express-session": "^1.12.1",
     "express-state": "^1.2.0",
-    "express-validator": "^4.3.0",
+    "express-validator": "^5.0.0",
     "fetchr": "~0.5.12",
     "font-awesome": "^4.7.0",
     "frameguard": "^3.0.0",