FIX: Make migrations work with Discourse stable

FIX: Make migrations work with Discourse stable

diff --git a/db/migrate/20191031193436_remove_old_akismet_states.rb b/db/migrate/20191031193436_remove_old_akismet_states.rb
index 22d479e..966f2eb 100644
--- a/db/migrate/20191031193436_remove_old_akismet_states.rb
+++ b/db/migrate/20191031193436_remove_old_akismet_states.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class RemoveOldAkismetStates < ActiveRecord::Migration[6.0]
+class RemoveOldAkismetStates < ActiveRecord::Migration[5.2]
   def up
     DB.exec(<<~SQL, updated_at: 5.minutes.ago
       DELETE FROM post_custom_fields

GitHub sha: d2503ae6