bugfix: adding missing access control allow origin header

@calummackervoy : that fixes the "Blocked request" error from my tests.

Do you agree with that ?

djangoldp_polls/views.py

@@ -16,12 +16,14 @@ class CanVoteOnPollViewSet(APIView):
 
     def get(self, request, pk):
         '''returns True if the user can vote, or False if they have already voted'''
+        headers = {"Access-Control-Allow-Origin" : request.META.get('HTTP_ORIGIN')}
+
         try:
             poll = Poll.objects.get(pk=pk)
             can_vote = True
             if Vote.objects.filter(relatedPoll=poll, user=request.user).exists():
                 can_vote = False
-            return Response(can_vote, status=status.HTTP_200_OK)
+            return Response(can_vote, status=status.HTTP_200_OK, headers=headers)
 
         except Poll.DoesNotExist:
             return Response(data={'error': {'poll': ['Could not find poll with this ID!']}},