feat(demo): update RXJS from "^6.6.7" to "^7.8.1" for ng13

Author: mhenkens

demo-app/ng13/package-lock.json

@@ -30,7 +30,7 @@
     "eligrey-classlist-js-polyfill": "1.2.20180112",
     "material-design-icons": "^3.0.1",
     "normalize.css": "^8.0.1",
-    "rxjs": "^6.6.7",
+    "rxjs": "^7.8.1",
     "tslib": "^2.0.0",
     "zone.js": "~0.11.4"
   },