title: TypeError: __init__() got an unexpected keyword argument 'on_delete'
body: <p>I built a model:</p>
  
  <pre><code>class Channel(models.Model):
      title = models.CharField(max_length=255, unique=True)
      slug = models.SlugField(allow_unicode=True, unique=True)
      description = models.TextField(blank=True, default='')
      description_html = models.TextField(editable=False, default='', 
  blank=True)
      subscribers = models.ManyToManyField(User, 
  through="ChannelMembers", on_delete=models.CASCADE,)
  </code></pre>
  
  <p>When I do makemigration it say :</p>
  
  <pre><code>TypeError: __init__() got an unexpected keyword argument 'on_delete'
  </code></pre>
  
  <p>And when a delete the <strong>on_delete</strong> it say:</p>
  
  <pre><code>TypeError: __init__() missing 1 required positional argument: 'on_delete'
  </code></pre>
  
  <p>What's worng?</p>