Define display_subsciption_reference short description for admin view.

coin/offers/models.py

@@ -109,6 +109,7 @@ class OfferSubscription(models.Model):
 
     def display_subsciption_reference(self):
         return settings.SUBSCRIPTION_REFERENCE.format(subsciption=self)
+    display_subsciption_reference.short_description = 'Référence'
 
     def __unicode__(self):
         return '%s - %s - %s' % (self.member, self.offer.name,