title: How can I set notification sound when app is not running in React-Native firebase
body: <p>I'm trying to make notification ringing when app is not running in IOS.</p>
  
  <p>Here is my code.</p>
  
  <pre><code>  this.notificationListener = firebase.notifications().onNotification((notification: Notification) =&gt; {
  
      // SET SYSTEM DEFAULT SOUND!
      notification.setSound("default");
      firebase.notifications().displayNotification(notification);
  
    });
  </code></pre>
  
  <p>When app is in background or foreground ( Maybe I can say 'app is running'), notification rings well.</p>
  
  <p>Should I need to use other listener?
  Or should I need to add my own sound file for ringing?</p>