Added separate assertion for Opencv2 and 3
Added separate assertion for Opencv2 and 3

Size marker area as calculated using moments have different values in OpenCV 2 and 3

stiphyMT/plantcv,stiphyMT/plantcv,danforthcenter/plantcv,stiphyMT/plantcv,danforthcenter/plantcv,danforthcenter/plantcv