#360: Improve code sample for unregistered device token detection

Author: eladnava

README.md

@@ -126,12 +126,12 @@ sender.send(message, { registrationTokens: registrationTokens }, 10, function (e
   else    console.log(response);
 });
 
-// Q: I need to remove all "bad" token from my database, how do I do that?
+// Q: I need to remove all expired / unregistered tokens from my database, how do I do that?
 //    The results-array does not contain any tokens!
 // A: The array of tokens used for sending will match the array of results, so you can cross-check them.
 sender.send(message, { registrationTokens: registrationTokens }, function (err, response) {
-  var failed_tokens = registrationTokens.filter((token, i) => response.results[i].error != null);
-  console.log('These tokens are no longer ok:', failed_tokens);
+  var failed_tokens = registrationTokens.filter((token, i) => response.results[i].error === 'NotRegistered');
+  console.log('These tokens are no longer registered:', failed_tokens);
 });
 ```
 ## Recipients