IOU matrix for Hungarian matching issue

[vladimir-tracxpoint]

It seems https://github.com/yasenh/sort-cpp/blob/1dcafbaa43513bfe8d80a18894fee829a40ba408/src/tracker.cpp#L37 does not work correct in some cases due to negative values. It's better to use matrix(i, j) = 1. - iou_matrix[i][j];