Make `check_files` more generic

[PetrochukM]

Line:

PyTorch-NLP/torchnlp/download.py

Line 126 in be1a08e

def download_file_maybe_extract(url, directory, filename=None, extension=None, check_files=[]):

Instead of check_files, we could check that particular path exist. That'll enable us to check for particular directories, as well.

[Kkuntal990]

Hey can I take this up?