title: Property 'from' does not exist on type 'typeof Observable', angular 6?
body: <p>I updated my angular 5.2.10 project to angular 6.<br>
  I did step by step <code>https://update.angular.io/</code>, everything is OK unless <code>Observable.from</code><br>
  In a service I used <code>Observable.from(this.user)</code> as following:</p>
  
  <pre><code>import { Observable } from 'rxjs/Observable';
  ...
  Observable.from(this.users)// this.users is an array
  </code></pre>
  
  <p>It was OK, but in angular 6 the following error occurred</p>
  
  <pre><code>Property 'from' does not exist on type 'typeof Observable'
  </code></pre>
  
  <p>I changed it as follows </p>
  
  <pre><code>import { Observable, from } from 'rxjs';
  </code></pre>
  
  <p>But no change and error occurred again!</p>