title: Angular 6 router.events.filter 'filter' does not exist on type 'Observable<Event>'
body: <p>I have finished to update my App to Angular 6 (it was in 5.2 version).</p>
  
  <p>I got an error syntax in :</p>
  
  <pre><code>import { Router, ActivatedRoute, NavigationEnd } from '@angular/router';
  import { filter } from 'rxjs/operators';
  ...
  constructor(private router: Router) {}
  
  this.router.events.filter
        (event =&gt; event instanceof NavigationEnd).subscribe((res) =&gt; 
      {
        // DO something
      });
  </code></pre>
  
  <blockquote>
    <p>error TS2339: Property 'filter' does not exist on type
    'Observable'.</p>
  </blockquote>
  
  <p>what's the right syntax in Angular 6 ?</p>
  
  <p>thanks</p>