🐛 Bug

In the hub.py, line 169 should be preceded by:
cached_zipfile.close()
Otherwise on Windows, it will crash with PermissionException

To Reproduce

Steps to reproduce the behavior:

1. Call torch.hub.load() on external repo on windows

File "...\python36pytorch\lib\site-packages\torch\hub.py", line 83, in _remove_if_exists
os.remove(path)
PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: '.../.cache\torch\hub\master.zip'