Demo Notebook Error:
🐛 Bug
trainer.fit(gan_model) 
ValueError: Your LightningModule defines 2 optimizers but training_step is missing the "optimizer_idx" argument.
To Reproduce
Steps to reproduce the behavior:

Go to this link.
Run the cell
Scroll down .
See error



PyTorch Version (e.g., 1.0): 1.4.0
OS (e.g., Linux): Linux
How you installed PyTorch (conda, pip, source): pip
Build command you used (if compiling from source):
Python version: 3.6
CUDA/cuDNN version:
GPU models and configuration:
Any other relevant information:

Additional context
This is the exact demo notebook.