'async' is a reserved word in Python 3.7. Cuda has shifted to 'non_blocking' instead. pytorch/pytorch#4999

flake8 testing of https://github.com/Scitator/prometheus on Python 3.7.0

$ flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics

./losses/unet.py:8:23: E999 SyntaxError: invalid syntax
    return x.cuda(async=True) if torch.cuda.is_available() else x
                      ^
1     E999 SyntaxError: invalid syntax
1