A bug in parameters of OpenCV testing

[weitong8591]

Hi!

In 'test_opencv.py', opencv_flag='USAC_MAGSAC' is not consistent with function 'opencv_flag', which should be 'MAGSAC'.

homography-benchmark/test_opencv.py

Line 134 in 7e18721

parser.add_argument("--opencv_flag", type=str, default="RANSAC", choices=["RANSAC", "LMEDS", "RHO", "USAC_MAGSAC"])