title: Nested Serializer not showing up
body: <p>I am trying to update my serializers in my drf project to be shown in a nested way. The two models in question are Image and Gallery, images are related to Galleries.</p>
  
  <p>I tried following <a href="https://www.django-rest-framework.org/api-guide/relations/#nested-relationships" rel="noreferrer">https://www.django-rest-framework.org/api-guide/relations/#nested-relationships</a>, but i am not entirely sure why it is not working.</p>
  
  <p>Below is models.py</p>
  
  <pre class="lang-py prettyprint-override"><code>class Gallery(models.Model):
      title = models.CharField(max_length=30)
      author = models.ForeignKey(User, on_delete=models.CASCADE)
      created_on = models.DateTimeField(auto_now_add=True, blank=True)
      modified_on = models.DateTimeField(auto_now=True, blank=True)
  
      def __str__(self):
          return self.title
  
  
  class Image(models.Model):
      gallery_id = models.ForeignKey(Gallery, on_delete=models.CASCADE)
      img = models.ImageField(upload_to='images/')
      created_on = models.DateTimeField(auto_now_add=True, blank=True)
  </code></pre>
  
  <p>serializers.py</p>
  
  <pre class="lang-py prettyprint-override"><code>class ImageSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Image
          fields = ["gallery_id", "img", "created_on", "id"]
  
  
  class GallerySerializer(serializers.HyperlinkedModelSerializer):
      image = ImageSerializer(many=True, read_only=True)
  
      def validate(self, data):
          # Check if user id is equal object id before creation or if SuperUser
          request = self.context.get("request")
          if request.user.id != data["author"].id and request.user.is_superuser is not True:
              raise ValidationError("Unauthorized User Post")
          return data
  
      class Meta:
          model = Gallery
          fields = ["title", "author", "created_on", "modified_on", "image", "id"]
  </code></pre>
  
  <p>Expecting outcome would be</p>
  
  <pre><code>[
    {
      "title": "test_1",
      "author": "http://127.0.0.1:8000/api/users/2/",
      "created_on": "2019-08-19T09:13:45.107658Z",
      "modified_on": "2019-08-19T09:13:45.107731Z",
      "image": [
        {
          "gallery_id": "http://127.0.0.1:8000/api/galleries/24/",
          "img": "http://127.0.0.1:8000/media/images/angga-tantama-background-art-minimalism.jpg",
          "created_on": "2019-08-20T09:17:31.790901Z",
          "id": 6
        },
        {
          "gallery_id": "http://127.0.0.1:8000/api/galleries/24/",
          "img": "http://127.0.0.1:8000/media/images/art-vector-background-illustration-minimalism-angga-tantam-2.jpg",
          "created_on": "2019-08-20T09:31:40.505035Z",
          "id": 7
        }
      ]
      "id": 24
    },
    {
      "title": "test_2",
      "author": "http://127.0.0.1:8000/api/users/2/",
      "created_on": "2019-08-20T09:42:09.448974Z",
      "modified_on": "2019-08-20T09:42:09.449042Z",
      "id": 27
    }
  ]
  </code></pre>