update also user_creations

db/migrate/20190517114808_add_default_salt.rb

@@ -7,10 +7,16 @@ migration(
     alter_table(:users) do
       set_column_default :salt, ''
     end
+    alter_table(:user_creations) do
+      set_column_default :salt, ''
+    end
   end,
   Proc.new do
     alter_table(:users) do
       set_column_default :salt, nil
     end
+    alter_table(:user_creations) do
+      set_column_default :salt, nil
+    end
   end
 )