title: custom sound not working in unnotificationrequest ios 10 objC
body: <p>custom sound not working in unnotificationrequest - iOS 10</p>
  <p>I tried :</p>
  <h2>[UNNotificationSound soundNamed:@&quot;Alarm.mp3&quot;]</h2>
  <p>or</p>
  <h2>[UNNotificationSound soundNamed:@&quot;Alarm&quot;]</h2>
  <p>and the file is exist in bundle or Library/Sounds
  but always played default sound when app is in background.
  is anybody know why?</p>