Fix commit 5e8abe83 (stupid mistake)

coin/offers/backends.py

@@ -6,8 +6,10 @@ repetitive tasks."""
 from django.core.exceptions import ValidationError
 from django.db.models import Q
 
+from coin.offers.models import OfferSubscription
 
-def ValidateBackendType(object):
+
+class ValidateBackendType(object):
     """Helper validator for configuration backends.
 
     It ensures that the related subscription has the right backend