text: Title: Easy way to build a nested dict from factory?
  Body: #### The problem
  
  My situation is similar to this one raised https://github.com/FactoryBoy/factory_boy/issues/68#issuecomment-363268477
  
  I have nested factories that use SubFactory
  
  When I want to use factory.build to create a dict, the nested factory comes out as object rather than as a dict.
  
  #### Proposed solution
  Is there a way to improve with a `build_nested_dict` function or there's a workaround?
  
  