Update dependency rxjs to v7

Author: renovate[bot]

package.json

@@ -18,7 +18,7 @@
     "es6-shim": "^0.35.0",
     "materialize-css": "^0.100.0",
     "reflect-metadata": "0.1.13",
-    "rxjs": "5.5.12",
+    "rxjs": "7.8.2",
     "systemjs": "0.21.6",
     "zone.js": "0.11.4"
   },