Clear settings cache after migration

src/pretix/base/migrations/0061_auto_20170521_0942.py

@@ -2,6 +2,7 @@
 # Generated by Django 1.10.7 on 2017-05-21 09:42
 from __future__ import unicode_literals
 
+from django.core.cache import cache
 from django.db import migrations
 
 
@@ -12,6 +13,7 @@ def rename_placeholder(app, schema_editor):
         if setting.key == 'mail_text_order_placed':
             new_value = setting.value.replace('{paymentinfo}', '{payment_info}')
             setting.value = new_value
+            cache.delete('hierarkey_{}_{}'.format('event', setting.object_id))
             setting.save()
 
 
@@ -21,5 +23,5 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.RunPython(rename_placeholder)
+        migrations.RunPython(rename_placeholder, migrations.RunPython.noop)
     ]