Undefined name 'PPGANTrainer' in DCGAN_trainer.py

[cclauss]

flake8 testing of https://github.com/facebookresearch/pytorch_GAN_zoo on Python 3.7.1

$ flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics

./models/trainer/DCGAN_trainer.py:19:16: F821 undefined name 'PPGANTrainer'
        return PPGANTrainer._defaultConfig
               ^
1     F821 undefined name 'PPGANTrainer'
1

E901,E999,F821,F822,F823 are the "showstopper" flake8 issues that can halt the runtime with a SyntaxError, NameError, etc. These 5 are different from most other flake8 issues which are merely "style violations" -- useful for readability but they do not effect runtime safety.

• F821: undefined name name
• F822: undefined name name in __all__
• F823: local variable name referenced before assignment
• E901: SyntaxError or IndentationError
• E999: SyntaxError -- failed to compile a file into an Abstract Syntax Tree

[Molugan]

https://github.com/facebookresearch/pytorch_GAN_zoo/pull/55