Build with OpenCV version >4.0

[nofreewill42]

Build fails, needs cv:: before CV_HSV2BGR after OpenCV version 4.0, at least that's what I suppose based on the following issuecomment: NVIDIA/DALI#735 (comment)

[LmitchellSTLA]

Change line to: cv::cvtColor(color, color_bar, cv::COLOR_HSV2BGR);
also add initialization at top: #include <random>

[chadrs2]

This what I added to my fork of this repo as well. Everything else should work