title: ng2-completer remote data with custom header is not working
body: <p>I am trying to use ng2-completer in Angular5. However I am not able to post custom header with it. I am trying to replicate <a href="https://github.com/oferh/ng2-completer/issues/241" rel="nofollow noreferrer">this</a></p>
  
  <p>My HTML code is as followed:</p>
  
  <pre><code>&lt;ng2-completer [inputClass]="{'form-control': true, 'has-error': !Name.valid &amp;&amp; Name.touched}"
                                 [(ngModel)]="searchStr"
                                 [datasource]="dataService"
                                 formControlName="Name"
                                 [minSearchLength]="3"
                                 autoMatch="true"
                                 clearUnselected="true"&gt;&lt;/ng2-completer&gt;
  </code></pre>
  
  <p>my component is as follows:</p>
  
  <pre><code>protected searchStr: string;
  headers: any;
  protected dataService: RemoteData;`
  
  
  
  
  constructor(private completerService: CompleterService, private url: UrlService) {
          this.headers = new Headers();
          const options = new RequestOptions({ headers: this.headers });
          options.headers.set('Content-Type', 'application/json');
          options.headers.set('Authorization', 'xxx');
          this.dataService = completerService.remote(url.data_url, 'name', 'name');
          this.dataRemote.requestOptions(options);
  
  }
  </code></pre>
  
  <p>This one is not sending my auth token. Please any one can help me? Thanks</p>