Ubuntu更换了source.list文件后，执行apt-get update，报如下错误
# apt-get update
Hit:1 http://cn.archive.ubuntu.com/ubuntu xenial InRelease
Hit:2 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:3 http://cn.archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit:4 http://cn.archive.ubuntu.com/ubuntu xenial-backports InRelease
Reading package lists... Done
E: The method driver /usr/lib/apt/methods/https could not be found.
N: Is the package apt-transport-https installed?
E: Failed to fetch https://download.docker.com/linux/ubuntu/dists/xenial/InRelease
E: Some index files failed to download. They have been ignored, or old ones used instead.解决方法：apt-get install -y apt-transport-https
建议在替换source.list 之前就执行apt-get install -y apt-transport-https
