message: docs(): update firebase config with default service worker filename
  The example Firebase config shows **sw.js** as the name of the service worker for which a cache policy should be set. However, the default filename used by is **ngsw-worker.js**. This change reflects the default filename.
diff: @@ -67,7 +67,7 @@ The last thing needed is to make sure caching headers are being set correctly. T
  ]
  },
  {
  - "source": "sw.js",
  + "source": "ngsw-worker.js",
  "headers": [
  {
  "key": "Cache-Control",
  