linux alpine 安装慢、apk add慢，更换国内源

转自：https://www.cnblogs.com/will-xz/p/13380144.html

阿里镜像

sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories

科大镜像

sed -i 's/dl-cdn.alpinelinux.org/mirrors.ustc.edu.cn/g' /etc/apk/repositories