gpu number

Hi, when I run the python run.py --num_workers 16 --env simple_mnist there are no output,and then I use tmux attach -t spiral to check every work, and work-2 shows the error below:
File "/home/XX/SPIRAL-tensorflow-master/models/discriminator.py", line 138, in build_optim
self.var_list += self.opt.variables()
AttributeError: 'AdamOptimizer' object has no attribute 'variables'

Do you know the reason and how to solve it? I use tensorflow1.4.
another question, is this project must be run with two GPUs?
Thank you!

Start with the run.py command and models/discriminator.py at line 138, then compare the reported AdamOptimizer error with the TensorFlow 1.4 API. Confirm whether the command completes without the worker failure and document the project's GPU requirements.

Written by the indexing model from the issue text.