title: APP_INITIALIZER not work in angular6 library
body: <p>I create an angular6 library call mapModule, and be imported into app module, now I want to do something before load mapModule, so I try to add <strong>APP_INITIALIZER</strong> in this library :</p>
  
  <pre><code>export function StartupServiceFactory2(mapConfigService: MapConfigService) {
      const x = 2 + 2; 
      console.log(x);
      return () =&gt; mapConfigService.readConfig();
  }
  </code></pre>
  
  <p>but it doesn't work</p>