Fixed typo in JSONResponseMixin example.

Author: gabrielgrant

docs/topics/class-based-views/index.txt

@@ -93,13 +93,13 @@ conversion to JSON once.
 For example, a simple JSON mixin might look something like this::
 
  import json
- from django import http
+ from django.http import HttpResponse
 
  class JSONResponseMixin(object):
  """
  A mixin that can be used to render a JSON response.
  """
- reponse_class = HTTPResponse
+ response_class = HttpResponse
 
  def render_to_response(self, context, **response_kwargs):
  """