Mac上使用brew update会卡住的问题
brew默认的源是Github，会非常慢，建议换为国内的源。推荐中科大的镜像源，比较全面.
解决方案
Homebrew
Homebrew源代码仓库
替换源地址:
cd "$(brew --repo)" git remote set-url origin https://mirrors.ustc.edu.cn/brew.git
重置为官方地址:
cd "$(brew --repo)" git remote set-url origin https://github.com/Homebrew/brew.git
Homebrew Bottles
Homebrew预编译二进制软件包
在运行brew, 前设置环境变量HOMEBREW_BOTTLE_DOMAIN，值为https://mirrors.ustc.edu.cn/homebrew-bottles
替换源地址:
bash:
echo 'export HOMEBREW_BOTTLE_DOMAIN=https://mirrors.ustc.edu.cn/homebrew-bottles' >> ~/.bash_profile source ~/.bash_profile
zsh:
echo 'export HOMEBREW_BOTTLE_DOMAIN=https://mirrors.ustc.edu.cn/homebrew-bottles' >> ~/.zshrc source ~/.zshrc
Homebrew Core
Homebrew核心软件仓库
替换源地址:
cd "$(brew --repo)/Library/Taps/homebrew/homebrew-core" git remote set-url origin https://mirrors.ustc.edu.cn/homebrew-core.git
重置为官方地址:
cd "$(brew --repo)/Library/Taps/homebrew/homebrew-core" git remote set-url origin https://github.com/Homebrew/homebrew-core
Homebrew Cask
Homebrew cask软件仓库，提供macOS应用和大型二进制文件
替换源地址:
cd "$(brew --repo)"/Library/Taps/homebrew/homebrew-cask git remote set-url origin https://mirrors.ustc.edu.cn/homebrew-cask.git
重置为官方地址:
cd "$(brew --repo)"/Library/Taps/homebrew/homebrew-cask git remote set-url origin https://github.com/Homebrew/homebrew-cask
