Update dependency helmet to v6

Author: renovate[bot]

package-lock.json

@@ -19,7 +19,7 @@
     "express": "4.18.1",
     "express-session": "1.17.3",
     "express-validator": "6.14.2",
-    "helmet": "3.23.3",
+    "helmet": "6.0.0",
     "html5shiv": "3.7.3",
     "http-errors": "1.8.1",
     "lodash": "4.17.21",