Fixed typo in document.
Fixed typo in document.

Signed-off-by: Han Qiang <5a8b3afa957cf56fdf01441139cebffd1f379d6f@gmail.com>

apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,apavlenko/opencv