title: Ionic2 ion-range not updating with ngModel
body: <p>My Ionic Info :</p>
  
  <p>Cordova CLI : 6.3.1</p>
  
  <p>Ionic Framework Version : 2.0.0-beta.11</p>
  
  <p>Ionic CLI version : 2.1.0-beta.3</p>
  
  <p>Ionic App Lib Version 2.0.0-beta.20</p>
  
  <p>Html :</p>
  
  <pre><code>&lt;ion-content padding&gt;
      &lt;form [formGroup]="myForm" (ngSubmit)="submitFunction()"&gt;   
          &lt;ion-item&gt;
              &lt;ion-range [(ngModel)]="myRange" name="formRange" formControlname="formRange"&gt;&lt;/ion-range&gt;
          &lt;/ion-item&gt;
      &lt;/form&gt;
      &lt;button (click)="myFunction()"&gt; function &lt;/button&gt;
      {{myRange}}
  &lt;/ion-content&gt;
  </code></pre>
  
  <p>In the beginning, my ion-range input will show 2 and the {{myRange}} too</p>
  
  <p>When I'm trying to update it directly with the range, it's ok. The {{myRange}} show the correct value. But if I update it with a function it's not working.</p>
  
  <pre><code>constructor(private builder: FormBuilder) {
      this.myRange = 2;
      this.myForm = builder.group({
          'formRange':this.myRange,
      });  
  }
  public myFunction()
  {
      this.myRange = 9;
  }
  </code></pre>
  
  <p>The display of {{myRange}} will show 9, but the ion-range input will still show 2.</p>
  
  <p>Am I doing something wrong ?</p>