Add missing information for `id` field when used with `select`

As given in the example:

```ruby
person.pets.select(:name)
# => [
 #<Pet id: nil, name: "Fancy-Fancy">,
 #<Pet id: nil, name: "Spook">,
 #<Pet id: nil, name: "Choo-Choo">
#]
```
So calling on `person.pets.select(:name).first.id` will not raise:
```ruby
ActiveModel::MissingAttributeError: missing attribute: id
```