修改Ubuntu的apt-get源为国内镜像源

• sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
• sudo vim /etc/apt/sources.list
  deb http://mirrors.aliyuncs.com/ubuntu/ bionic main restricted universe multiverse deb http://mirrors.aliyuncs.com/ubuntu/ bionic-security main restricted universe multiverse deb http://mirrors.aliyuncs.com/ubuntu/ bionic-updates main restricted universe multiverse deb http://mirrors.aliyuncs.com/ubuntu/ bionic-proposed main restricted universe multiverse deb http://mirrors.aliyuncs.com/ubuntu/ bionic-backports main restricted universe multiverse deb-src http://mirrors.aliyuncs.com/ubuntu/ bionic main restricted universe multiverse deb-src http://mirrors.aliyuncs.com/ubuntu/ bionic-security main restricted universe multiverse deb-src http://mirrors.aliyuncs.com/ubuntu/ bionic-updates main restricted universe multiverse deb-src http://mirrors.aliyuncs.com/ubuntu/ bionic-proposed main restricted universe multiverse deb-src http://mirrors.aliyuncs.com/ubuntu/ bionic-backports main restricted universe multiverse
• 运行sudo apt-get update