message: refactor(service-worker): ensure compatibility with typescript strict flag
  As part of the `@angular/service-worker` package is made compatible
  with the TypeScript `--strict` flag. Read more about the strict flag [here](https://www.typescriptlang.org/docs/handbook/compiler-options.html)
  PR Close
diff: @@ -76,7 +76,7 @@ export class NgswCommChannel {
  const currentController = defer(() => of (serviceWorker.controller));
  const controllerWithChanges = concat(currentController, controllerChanges);
  - this.worker = controllerWithChanges.pipe(filter<ServiceWorker>(c => !!c));
  + this.worker = controllerWithChanges.pipe(filter((c): c is ServiceWorker => !!c));
  this.registration = <Observable<ServiceWorkerRegistration>>(
  this.worker.pipe(switchMap(() => serviceWorker.getRegistration())));
  