title: FormControl debounceTime not available in angular 5 (ionic 3)
body: <p>I just updated angular in ionic app from version 4 to 5. I have some search FormControl inputs that allow user to search a database via ajax requests.
  I used debounceTime() method to delay ajax search request but after angular upgrade this method is no longer available. I removed this method call but now a new request is made on every user key press on android. </p>
  
  <p>Is there any other way to achieve this delay?</p>
  
  <pre><code>this.searchControl.valueChanges
          .debounceTime(2000)
          .subscribe(search =&gt; this.getCities(search));
  </code></pre>