Fix typo (and thus, crash) on payment deletion

Only for instances with settings.HANDLE_BALANCE set to True

coin/billing/models.py

@@ -629,7 +629,7 @@ def paymentallocation_deleted(sender, instance, **kwargs):
 def payment_deleted(sender, instance, **kwargs):
 
     accounting_log.info(
-        "Deleted payment {} (Date: {}, Member: {}, Amount: {}, Label: {}).".forma(
+        "Deleted payment {} (Date: {}, Member: {}, Amount: {}, Label: {}).".format(
             instance.pk, instance.date, instance.member, instance.amount, instance.label))
 
     member = instance.member