title: angular2 Pipe expression on [ngClass] not working
body: <p>I have a Pipe to capitalize first letter in dynamic input string </p>
  
  <pre><code>@Pipe({
    name: 'capitalize'
  })
  export class CapitalizePipe implements PipeTransform {
  
  transform(value: string, args: any[]): string {
  if (value === null) return 'Not assigned';
  return value.charAt(0).toUpperCase() + value.slice(1);
   }
  }
  </code></pre>
  
  <p><strong>Pipe is not accepting inside [ngClass] like</strong></p>
  
  <blockquote>
    <p>[ngClass]="data.color | capitalize">   // data.color is json input --> not capitalizing input string </p>
  </blockquote>
  
  <pre><code>&lt;md-input-container&gt;
      &lt;input mdInput placeholder="Severity" value="{{ data.color }}" readonly&gt;
      &lt;md-icon [ngClass]="data.color+''|capitalize"&gt;&lt;/md-icon&gt;
    &lt;/md-input-container&gt;
  </code></pre>
  
  <p>When i print as {{data.color | capitalize}} it is working fine input = "name" 
  prints as "Name". Any help would be great.</p>