Nested routes with namespace appears to be broken in 0.6

I have an admin page that looks like the following

```ruby
ActiveAdmin.register CloudAccount::Base, as: 'Cloud Account' do
```

I have a child admin page that that defines the parent as follows

``` ruby
belongs_to :cloud_account, parent_class: CloudAccount::Base, instance_name: :fileable, optional: :true
```

Nested routes worked in 0.5.x for this model (ie. /admin/cloud_accounts/:id/file_actions), however in 0.6 I get

undefined method `find_by_id' for CloudAccount:Module

Looks like for some reason it's using the module and not recognizing the "parent_class" specifier.