title: NgbModal.open not working in Angular 4
body: <p>I want to display a message in a modal using angular 4.0.0 and 
  ng-bootstrap 1.0.0-beta.4 but it does not display the modal.</p>
  
  <p>app-module.ts</p>
  
  <pre><code>@NgModule({
  // ...
  declarations: [
    LoginComponent
  ],
  imports: [
  // ...
    NgbModule.forRoot()
  ],
  entryComponents: [LoginComponent],
  })
  export class AppModule { }
  </code></pre>
  
  <p>login.component.ts</p>
  
  <pre><code>@Component({
    selector: 'app-login',
    templateUrl: './login.component.html',
    styleUrls: ['./login.component.css']
  })
  export class LoginComponent {
     @ViewChild('examplemodal')
     private modalRef: TemplateRef&lt;any&gt;;
  
     constructor(private modalService: NgbModal) { }
  
     //.... some event that fires onModalRequest() 
  
     onModalRequest(): void {
      const modalRef = this.modalService.open(this.modalRef); //Not working
  
      modalRef.result.then((result) =&gt; {
        console.log(result);
        console.log('closed');
      }).catch( (result) =&gt; {
        console.log(result);
        console.log('cancelling');
      });
    }
  }
  </code></pre>
  
  <p>examplemodal.html</p>
  
  <pre><code>&lt;ng-template #examplemodal&gt;
    &lt;div class="modal"&gt;
      stuff here...
    &lt;/div&gt;
  &lt;/ng-template&gt;
  </code></pre>
  
  <p>Any help please?</p>