Ubuntu18.04编译OpenCV时遇到无法下载ADE的问题

安装OpenCV过程中编译时出现下载ADE失败的问题
报错如下：

-- ADE: Downloading v0.1.2a.zip from https://github.com/opencv/ade/archive/v0.1.2a.zip
-- Try 1 failed
CMake Warning at cmake/OpenCVDownload.cmake:248 (message):
  ADE: Download failed: 28;"Timeout was reached"
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问题出现原因：

github访问超时
解决方法：
编译时增加Cmake选项，将下载源更改为GitCode镜像

-D OPENCV_DOWNLOAD_MIRROR_ID=gitcode
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