title: Not receiving Firebase Cloud Messaging delivery receipts
body: <p>I am sending the following message through fcm xmpp client. But I am not getting delivery receipt for the delivered messages.</p>
  
  <p>I am using <code>node-xcs</code> node package for sending XMPP message.</p>
  
  <pre><code>var Sender = require('node-xcs').Sender;
  var Message = require('node-xcs').Message;
  var Notification = require('node-xcs').Notification;
  var Result = require('node-xcs').Result;
  var xcs = new Sender('123', 'xxxx', 1);
  const uuidv4 = require('uuid/v4');
  xcs.on('message', function(messageId, from, data, category) {
      console.log('received message', arguments);
  }); 
  
  
  xcs.on('receipt', function(messageId, from,  data, category){
      console.log(messageId,'dsafdsafdsaf')
  });
  
  xcs.on('connected', function(){console.log('connected')});
  xcs.on('disconnected', function(){console.log('disconnected')});
  xcs.on('online', function(){console.log('online')});
  xcs.on('error', console.error);
  xcs.on('message-error', function(){console.log('message-error')});
  
  var notification = new Notification("./logo.png")
      .title("Hello buddy!")
      .clickAction("https://github.com/guness/node-xcs/blob/master/google/Notification.js")
      .body("test_body")
      .build();
  
  var message = new Message(uuidv4())
      .priority("high")
      .dryRun(false)
      .deliveryReceiptRequested(true)
      .notification(notification)
      .build();
  
  xcs.sendNoRetry(message, 'token', function(result) {
      if (result.getError()) {
          console.error(result.getErrorDescription());
      } else {
          console.log("message sent: #" + result.getMessageId());
      }
  });
  </code></pre>
  
  <p>Below is the XMPP message sent from the package</p>
  
  <pre><code>&lt;gcm xmlns="google:mobile:data"&gt;{
    "to": "token",
    "message_id": "59171fc6-42ad-4f22-812f-d0c4f7fa63d0",
    "priority": "high",
    "delivery_receipt_requested": true,
    "notification": {
      "body": "test_body",
      "click_action": "https://github.com/guness/node-xcs/blob/master/google/Notification.js",
      "icon": "./logo.png",
      "title": "Hello buddy!"
    }
  }&lt;/gcm&gt;
  </code></pre>
  
  <p>I am getting <code>ack</code>, but I am not getting Delivery receipt, Why is the delivery receipt not coming even if the message is delivered?</p>