替换Alpine仓库源

直接替换 /etc/apk/repositories

#/media/cdrom/apks
http://mirrors.tuna.tsinghua.edu.cn/alpine/v3.8/main  
http://mirrors.tuna.tsinghua.edu.cn/alpine/v3.8/community  
http://mirrors.tuna.tsinghua.edu.cn/alpine/edge/main  
http://mirrors.tuna.tsinghua.edu.cn/alpine/edge/community  
http://mirrors.tuna.tsinghua.edu.cn/alpine/edge/testing