Fix issue that scopes with same name got overridden

seems like scope methods are defined in one place and shared across all classes, so with same scope name it'll be overridden.

```ruby
class Recipe < Spyke::Base
  scope :published, -> { where(status: 'published') }
end

class Comment < Spyke::Base
end

Comment.respond_to?(:published) 
# => true
Comment.published
# => #<Spyke::Relation:0x007ff668109058 @klass=Comment, @options={:uri=>"/comments/:id"}, @params={:status=>"published"}>
```