title: Firebase InstanceID.instanceID().token() method is deprecated
body: <p>I am working with swift and firebase. Previously I was using following method to get firebase token which then I was using  to store into database to send notifications.</p>
  
  <pre><code>InstanceID.instanceID().token()
  </code></pre>
  
  <p>Now this method is showing as deprecated since i have updated my firebase.</p>
  
  <pre><code>'token()' is deprecated: Use instanceIDWithHandler: instead.
  </code></pre>
  
  <p>I don't know how to use <code>instanceIDWithHandler</code> i have tried following but don't know how to get token.</p>
  
  <pre><code>func instanceID(handler: @escaping InstanceIDResultHandler){
  
      }
  </code></pre>
  
  <p>Please help.
  Thank you in advance.</p>