It seems that the installed PyTorch and torchvision versions are not compatible.
I guess that torchvision might be in a newer version and tries to call torch.jit.annotations.Optional, which isn’t available in your (older) PyTorch installation.
Could you check the versions of both libs via:
print(torch.__version__)
print(torchvision.__version__)

And make sure to use the latest stable release or the nightly binaries for both?