text: Title: Create the list of object as response model, but being restplus complained not iterable
  Body: Hi, 
  I want to get response of list of object, like this
  [{"name":"aaa",
     "id": 3},
  {"name":"bbb",
     "id": 4}]
  CREATIVE_ASSET_MODEL = {"name" : String(), "id": Integer()}
  
  The model is 
  ASSETS_RESPONSE_MODEL = api_namespace.model('Response Model', List(Nested(model=CREATIVE_ASSET_MODEL)))
  
  But it complained the list is not iterable. 
  
  Make it a dict will work, like this:
  ASSETS_RESPONSE_MODEL = api_namespace.model('Response Model', {'result' : List(Nested(model=CREATIVE_ASSET_MODEL))
  })
  
  But I don't want to add the 'result' to the response, can anyone help me with this, thanks!