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"}>
```
not really sure what's going on here but I referred to [Her](https://github.com/remiprev/her/blob/4824f6f18e4de091fede948cf362728c851f3654/lib/her/model/orm.rb#L102) and it seemed working :sweat_smile: feel free to change it, the spec I added should be able to catch it