title: timeoutWith operator Angular 5 Httpcleint
body: <p>just startting to upgrade angular 2.0.0 to 5.2.0 . So i'm using HttpClient . 
  I want to use timeoutWith operator on <code>httpClient.get()</code>. All i get is  <code>Property 'timeoutWith' does not exist on type 'Observable&lt;Object&gt;'.</code></p>
  
  <pre><code>someFunction(){
   let someUrl = '.../../' ;
  return this._httpClient.get(url).timeoutWith(1000,this.throwTimeout()).catch(this.handleError);
  
  }
  </code></pre>
  
  <p>What am i doing wrong ? this was working with the previous httpmodule</p>
  
  <p>Thanks </p>