fix(deps): update dependency rxjs to v6.4.0

Author: renovate-bot

package-lock.json

@@ -18,7 +18,7 @@
     "core-js": "2.5.7",
     "meteor-node-stubs": "0.4.1",
     "meteor-rxjs": "0.4.14",
-    "rxjs": "6.3.3",
+    "rxjs": "6.4.0",
     "zone.js": "0.8.26"
   },
   "devDependencies": {