ubuntu16.04 execute apt-get update failed

Background: I want to install the vim editor, using sudo apt-get install vim has prompted the connection failed! (Firefox Internet access);
even if the replacement of almost all domestic sources (Tsinghua University, Ali and the like) or suggesting a connection failure;
Solution:
In https://mirrors.ustc.edu.cn/repogen/ through their own ubuntu version gets copied source updates, if not, use https, use HTTPS can effectively prevent domestic carriers cache hijacking.

Download sources.list can replace the original (/etc/apt/sources.list) of;