'async' is a reserved word in Python >= 3.7

[cclauss]

flake8 testing of https://github.com/jantic/DeOldify on Python 3.7.1

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

./fastai/core.py:37:32: E999 SyntaxError: invalid syntax
    if cuda: a = to_gpu(a, async=True)
                               ^
./fastai/models/inceptionresnetv2.py:316:20: F821 undefined name 'pretrained_settings'
        settings = pretrained_settings['inceptionresnetv2'][pretrained]
                   ^
./fastai/models/inceptionresnetv2.py:321:17: F821 undefined name 'InceptionResNetV2'
        model = InceptionResNetV2(num_classes=1001)
                ^
./fastai/models/inceptionresnetv2.py:337:17: F821 undefined name 'InceptionResNetV2'
        model = InceptionResNetV2(num_classes=num_classes)
                ^
./fastai/models/cifar10/main_dxy.py:179:32: E999 SyntaxError: invalid syntax
      target = target.cuda(async=True)
                               ^
./fastai/models/cifar10/utils.py:114:32: F821 undefined name 'random'
  return string + '-{}'.format(random.randint(1, 10000))
                               ^
./fastai/models/cifar10/utils_kuangliu.py:17:18: F821 undefined name 'torch'
    dataloader = torch.utils.data.DataLoader(dataset, batch_size=1, shuffle=True, num_workers=2)
                 ^
./fastai/models/cifar10/utils_kuangliu.py:18:12: F821 undefined name 'torch'
    mean = torch.zeros(3)
           ^
./fastai/models/cifar10/utils_kuangliu.py:19:11: F821 undefined name 'torch'
    std = torch.zeros(3)
          ^
2     E999 SyntaxError: invalid syntax
7     F821 undefined name 'random'
9

[jantic]

Forgot to close this- merged this in a few days ago.