Add timestamps to category_expert_endorsements (PR #23)

I like using this proc for default here. It’s much cleaner than this

def change
  add_timestamps :category_expert_endorsements, null: true 

  # update the created/upated_at columns to some date

  change_column_null :category_expert_endorsements, :created_at, false
  change_column_null :category_expert_endorsements, :updated_at, false
end

GitHub