title: typeof XService is not assignable to type 'FactoryProvider'. Property 'provide' is missing
body: <p>I have an Angular 2 <code>NgModule</code> in a Ionic 2 mobile app defined like so:</p>
  
  <pre><code>@NgModule({
    declarations: [
      MyApp,
      HomePage,
    ],
    imports: [
      IonicModule.forRoot(MyApp)
    ],
    bootstrap: [IonicApp],
    entryComponents: [
      MyApp,
      HomePage,
    ],
    providers: [{provide: ErrorHandler, useClass: IonicErrorHandler}, VatRatesDbService]
  })
  export class AppModule {}
  </code></pre>
  
  <p>and the service defined this way:</p>
  
  <pre><code>import { Injectable } from '@angular/core';
  import * as PouchDB from 'pouchdb';
  
  @Injectable()
  export class VatRatesDbService {
  
    private _db;
  
    private constructor() {
      this._db = new PouchDB('rates.db', { adapter: 'websql' });
    }
  }
  </code></pre>
  
  <p>However, I'm getting the following error at runtime:</p>
  
  <blockquote>
    <p>Type 'typeof VatRatesDbService' is not assignable to type
    'FactoryProvider'. Property 'provide' is missing in type 'typeof
    VatRatesDbService'.</p>
  </blockquote>