PyTorch 1.6 function name modification

[Lornatang]

Error：

/home/unix/miniconda3/lib/python3.8/site-packages/torch/cuda/memory.py:344: FutureWarning: torch.cuda.memory_cached has been renamed to torch.cuda.memory_reserved

raw:

# for https://github.com/ultralytics/yolov5/blob/adaf1d8ac109f5c0977c27ceb3c2165a9c619cf2/train.py#L315
                mem = '%.3gG' % (torch.cuda.memory_cached() / 1E9 if torch.cuda.is_available() else 0)  # (GB)

new:

                mem = '%.3gG' % (torch.cuda.memory_reserved() / 1E9 if torch.cuda.is_available() else 0)  # (GB)

[glenn-jocher]

Thanks, I see the PR!