title: UUID Is not JSON Serializable (dumpdata)
body: <p>I'm having an issue with the command <code>dumpdata</code>. I'm using <a href="https://github.com/dcramer/django-uuidfield" rel="nofollow"><code>django-uuidfield</code></a> as primary key for a few of my models, however; whenever I try to run <code>dumpdata</code>, I run into the error </p>
  
  <p><code>TypeError: UUID('...') is not JSON serializable</code>.</p>
  
  <p>I found that inside of Django's <a href="https://github.com/django/django/blob/master/django/core/serializers/json.py#L87" rel="nofollow"><code>DjangoJSONEncoder</code></a> class that it doesn't check for the <code>UUID</code> object and will go to the <code>default()</code> of the parent class which throws the exception.</p>
  
  <p>When I added a check, it seemed to work properly without any errors or warnings.</p>
  
  <p>I'm not sure if that's a bug or I'm doing something wrong.</p>
  
  <p><strong>Note:</strong></p>
  
  <p>I didn't change any code inside <code>django-uuidfield</code>.</p>
  
  <p>Thanks.</p>
  
  <p><strong>Edit:</strong></p>
  
  <p>The <code>dumpdata</code> works for another model where the <code>uuidfield</code> is not set to <code>auto</code>. The one that doesn't work has the <code>uudfield</code> set to <code>auto</code>.</p>