```ruby
class HolidaySerializer < ActiveModel::Serializer
  attribute :title
  attribute :start do
    object.start_at
  end
  attribute :end do
    object.end_at
  end
end
```

Refactor holiday serializer to use built in aliasing
user
```ruby
class HolidaySerializer < ActiveModel::Serializer
  attribute :title
  attribute :start_at, key: :start
  attribute :end_at, key: :end
end
```
assistant