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

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-HELMETCSP-469436

Author: snyk-bot

package-lock.json

@@ -66,7 +66,7 @@
     "express": "4.17.1",
     "firebase": "6.2.0",
     "grpc": "1.21.1",
-    "helmet": "3.18.0",
+    "helmet": "3.21.1",
     "ng-animate": "0.3.4",
     "ng-lazyload-image": "5.1.2",
     "ngx-cookie": "4.1.2",