title: Allow partial update in serializer_class in Django REST
body: <p>I am trying to partially update my ProfileSerializer when i am making PATCH request. However i am not able to make it beacuse by default Serializer doesn't allow partial changes to be made. I am using Django Rest Framwork UpdateModelMixin to handle my patch request. Where can i set <code>partial=True</code> in my case?</p>
  <p>View:</p>
  <pre><code>class ProfileViewPartialUpdate(GenericAPIView, UpdateModelMixin):
      queryset = Profile.objects.all()
      serializer_class = ProfileSerializer
      lookup_field = 'token'
      lookup_url_kwarg = 'pk'
  
      def patch(self, request, *args, **kwargs):
          return self.partial_update(request, *args, **kwargs)
  </code></pre>
  <p>Serializer:</p>
  <pre><code>class ProfileSerializer(serializers.ModelSerializer):
      class Meta:
          model = Profile
          fields = ('token', 'bio', 'name', 'email', 'sport', 'location', 'image')
  </code></pre>