update digits_video.py

update digits_video.py

Following were the errors in the digits_video.py
     1 ) The code was not working because data type of x was float however in "cv2.rectangle" we require integer .
     2 ) After pressing the "esc" button the image windows did not destroy
So I amended following things:
     1 ) ~converted data type of x to int.~ Used Python integer division (//)
     2 ) used cv2.destroyAllWindows() to close all windows after the press of "esc" by user.