Ananoconda import cv2 ModuleNotFoundError無法安裝opencv（沒有cv2包）

Solving environment: failed with initial frozen solve. Retrying with flexible solve.
參考：
https://github.com/conda/conda/issues/9367

我是如此解決的

conda create --name FaceMaskDetection2 python=3.7
conda activate FaceMaskDetection2
conda install pytorch torchvision cpuonly -c pytorch#因爲我用pytorch，cpu（無gpu）win10
conda install -c menpo opencv