title: JMSSerializer - how to pass timezone to serialization
body: <p>I have setted timezone in <code>php.ini</code> file to <code>UTC</code> but in my app I have <code>Europe/Warsaw</code>. </p>
  
  <p>The question is: How to pass that 2nd timezone to JMS to use it for serialization <code>\DateTime</code> objects?
  I have tried something like this:</p>
  
  <pre><code>        date_default_timezone_set($timezone); //Europe/Warsaw
          $serializer = $this-&gt;get('jms_serializer');
          $data = $serializer-&gt;serialize($shift, 'json');
  </code></pre>
  
  <p>but it seems that in the first place <code>JMS</code> is looking for timezone in <code>php.ini</code> file because it returns <code>\DateTime</code> objects in format like this:</p>
  
  <pre><code>created_at:"2017-03-23T09:21:45+0000"
  date:"2017-03-24T00:00:00+0000"
  </code></pre>