Fix delete activities not federating

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -309,7 +309,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
 
   def delete(%Object{data: %{"id" => id, "actor" => actor}} = object, local \\ true) do
     user = User.get_cached_by_ap_id(actor)
-    to = object.data["to"] || [] ++ object.data["cc"] || []
+    to = (object.data["to"] || []) ++ (object.data["cc"] || [])
 
     data = %{
       "type" => "Delete",