fixes a typo in ThreadsService
fixes a typo in ThreadsService

ng-book/angular2-rxjs-chat,ahmadassaf/Angular-RxJS-Chat,ahmadassaf/Angular-RxJS-Chat,ahmadassaf/Angular-RxJS-Chat,ng-book/angular2-rxjs-chat,ng-book/angular2-rxjs-chat,ng-book/angular2-rxjs-chat