title: Angular 6 providedin doesn't work -> StaticInjectorError
body: <p>I'm trying to use 'providedin' feature in Angular but receive the error "StaticInjectorError(AppModule)[DashboardComponent -> DashboardService]:"</p>
  
  <pre><code>@Injectable({
    providedIn: DashboardModule
  })
  export class DashboardService {
    getContent() {
      return 'Dashboard Service works!!!';
    }
  }
  </code></pre>
  
  <p>Full demo <a href="https://stackblitz.com/edit/angular-kbkjet" rel="noreferrer">https://stackblitz.com/edit/angular-kbkjet</a>
  Thanks for you effort!</p>