`slugged` forced by `scoped`

It seems that the option `scoped` forces the use of `slugged`. As a result, it uses the wrong `query_method`. For example

```ruby
class Exam
  belongs_to :course

  extend FriendlyId

  friendly_id :title, use: :scoped, scope: :course
end
```

Here, `title` is a unique column, but if `ex` is an instance of `Exam`, `ee.friendly_id` will try to call `slug`.