import { Headers, Http } from '@angular/http';

@Injectable()
export class PublisherService{

    private publishersUrl = 'app/publisher';

    constructor(private http: Http) { }

    getPublishers(): Promise<Publisher[]>{
        return this.http.get(this.publishersUrl)
                   .toPromise()
                   .then(response => response.json().data) 
                   .catch(this.handleError);
    }
}    

Recibo este error:

La propiedad 'toPromise' no existe en el tipo 'Observable'.any