Fix cv2 version checking in motrackers.detectors.yolo.py

[taekim027]

Hello, wondering if the below line 26 in motrackers.detectors.yolo.py causes issues for anyone else.

        if cv2.__version__ == '4.6.0':

1. Because import cv2 as cv, I get a NameError: name 'cv2' is not defined when using this file. I believe changing the line to use cv instead of cv2 should fix the issue.
2. I believe the line should check for greater than or equal to 4.6.0. My version is 4.8.0 and I get IndexError: invalid index to scalar variable. when using the file as-is

TL;DR proposed fix:

        if cv.__version__ >= '4.6.0':

Thanks!

[paartheee]

issue fixed , thanks @taekim027

[adipandas]

Thanks for the contribution!