告别缓慢 为Debian更换国内的源

更换源为中科大

deb http://mirrors.ustc.edu.cn/debian stable main contrib non-free

deb-src http://mirrors.ustc.edu.cn/debian stable main contrib non-free

deb http://mirrors.ustc.edu.cn/debian stable-proposed-updates main contrib non-free

deb-src http://mirrors.ustc.edu.cn/debian stable-proposed-updates main contrib non-free