20-default.list Website may be down.

錯誤描述

ERROR: cannot download default sources list from:
https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list
Website may be down.

解決方法：修改DNS

1. Windows打開C:/windows/system32/drivers/etc/hosts，追加下面內容后刷新DNS緩存ipconfig /flushdns
2. Linux打開/etc/hosts，追加下面內容，無需刷新緩存
3. Mac打開/etc/hosts，追加下面內容，使用sudo killall -HUP mDNSResponder刷新DNS緩存

# GitHub Start
52.74.223.119     github.com
192.30.253.119    gist.github.com
54.169.195.247    api.github.com
185.199.111.153   assets-cdn.github.com
151.101.76.133    raw.githubusercontent.com
151.101.76.133    gist.githubusercontent.com
151.101.76.133    cloud.githubusercontent.com
151.101.76.133    camo.githubusercontent.com
151.101.76.133    avatars0.githubusercontent.com
151.101.76.133    avatars1.githubusercontent.com
151.101.76.133    avatars2.githubusercontent.com
151.101.76.133    avatars3.githubusercontent.com
151.101.76.133    avatars4.githubusercontent.com
151.101.76.133    avatars5.githubusercontent.com
151.101.76.133    avatars6.githubusercontent.com
151.101.76.133    avatars7.githubusercontent.com
151.101.76.133    avatars8.githubusercontent.com
# GitHub End

補充：（用來查詢域名解析地址的工具）
DNS查詢-站長工具: http://tool.chinaz.com/dns/
IP或域名查詢-查詢網: https://site.ip138.com/

參考文章：https://zhuanlan.zhihu.com/p/107691233