WebcamVideoStream.read should return tuple like cv.VideoCapture does

[crackwitz]

https://github.com/jrosebr1/imutils/blob/df65a77087548b5952431cc8006d66bcca7b1abc/imutils/video/webcamvideostream.py#L38

someone just showed up freenode's #opencv with this.

[mhmmdd]

This PR fixes this issue: #202