contour issue

[Aroxed]

Hi.
Thanks for the great project but I ran into the bug. I started the project as you described in the readme but there was an error:
digits_ocr.py:

displayCnt = None
....
lines 57-58:
if len(approx) == 4:
displayCnt = approx
displayCnt stays None!
and therefore
warped = four_point_transform(gray, displayCnt.reshape(4, 2))
doesn't work.

Could you please to fix that issue.

Thanks for your cool work again,
Andrii.