Require OpenCV V4.0
github gocv: https://github.com/hybridgroup/gocv
brew install pkg-config
brew install glog
brew install hybridgroup/tools/opencv
## data for face detect example
mkdir data
curl -L "https://github.com/hybridgroup/gocv/blob/master/data/haarcascade_frontalface_default.xml?raw=true" > data/haarcascade_frontalface_default.xml