title: Check if push is successful - angularfire2
body: <p>currently i develop an Ionic2 application which commuicates with a Firebase database. While updating a node sometimes it works and sometimes it doesn't.
  So i tired to handle the error with the following code:</p>
  
  <pre><code>this.db.list("/Events/" + this.eventID+ "/teilnehmer").push(this.userID)
          .then(resolve =&gt; {
            console.log('success');
          }, reject =&gt; {
            console.log('error');
          })
          .catch(reject =&gt; {
            console.log('catch');
          });
  </code></pre>
  
  <p>But even if i disconnect my internet connection there is no error thrown.
  Does someone of you know how i could handle an error if the push was not successful?</p>