Update dependency rxjs to v6.6.3

Author: renovate-bot

package-lock.json

@@ -29,7 +29,7 @@
     "hammerjs": "2.0.8",
     "ng-flash-messages": "0.3.0",
     "ngx-webstorage-service": "4.1.0",
-    "rxjs": "6.4.0",
+    "rxjs": "6.6.3",
     "tslib": "1.13.0",
     "zone.js": "0.9.1"
   },