fix name 'cleaners' is not defined

[linyueqian]

When I try to test the model using codes in 🪑 Basics, I came across an error. It can be fixed after changing the code in __init__.py

     67   for name in cleaner_names:
---> 68     cleaner = getattr(cleaners, name)
     69     if not cleaner:
     70       raise Exception('Unknown cleaner: %s' % name)

NameError: name 'cleaners' is not defined```