Add correct index.

priv/repo/migrations/20170620142420_add_object_activity_index_part_two.exs

@@ -0,0 +1,8 @@
+defmodule Pleroma.Repo.Migrations.AddObjectActivityIndexPartTwo do
+  use Ecto.Migration
+
+  def change do
+    drop index(:objects, ["(data->'object'->>'id')", "(data->>'type')"], name: :activities_create_objects_index)
+    create index(:activities, ["(data->'object'->>'id')", "(data->>'type')"], name: :activities_create_objects_index)
+  end
+end