解決方法
在終端輸入 sudo vim /etc/hosts 命令（必須用 sudo，以管理員的身份打開，不然無法修改 hosts 文件）
添加如下代碼：
# GitHub Start
# 192.30.253.112 github.com
# 192.30.253.119 gist.github.com
# 151.101.184.133 assets-cdn.github.com
# 151.101.184.133 raw.githubusercontent.com
# 151.101.184.133 gist.githubusercontent.com
# 151.101.184.133 cloud.githubusercontent.com
# 151.101.184.133 camo.githubusercontent.com
151.101.184.133 avatars0.githubusercontent.com
151.101.184.133 avatars1.githubusercontent.com
151.101.184.133 avatars2.githubusercontent.com
151.101.184.133 avatars3.githubusercontent.com
151.101.184.133 avatars4.githubusercontent.com
151.101.184.133 avatars5.githubusercontent.com
151.101.184.133 avatars6.githubusercontent.com
151.101.184.133 avatars7.githubusercontent.com
151.101.184.133 avatars8.githubusercontent.com
上圖爲什麼要註釋掉前面那幾行代碼，請看這裏