FIX: Allow '-1' value to delete_expired_event_posts_after site setting

FIX: Allow ‘-1’ value to delete_expired_event_posts_after site setting

diff --git a/config/settings.yml b/config/settings.yml
index cf16963..5ae059b 100644
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -6,4 +6,5 @@ plugins:
     default: ""
     client: true
   delete_expired_event_posts_after:
+    min: -1
     default: 1

GitHub sha: 654d8ebe