Fix #44 using content_type instead of mimetype

bt/views.py

@@ -284,7 +284,7 @@ class ViolationSearchView(SearchView):
 def get_attach(request,id):
     f = get_object_or_404(Attachment, pk=id)
     wrapper = FileWrapper(f.storage)
-    response=HttpResponse(wrapper, mimetype=f.type)
+    response=HttpResponse(wrapper, content_type=f.type)
     response['Content-Disposition'] = 'attachment; filename="%s"' % f.name
     response['Content-Length'] = f.storage.size
     return response