Brew update 慢

Brew update 慢
https://www.jianshu.com/p/62f1b963baa6
https://www.uedbox.com/post/57246/

第一步，替换brew.git

cd "$(brew --repo)"
git remote set-url origin https://mirrors.ustc.edu.cn/brew.git
第二步：替换homebrew-core.git

cd "$(brew --repo)/Library/Taps/homebrew/homebrew-core"
git remote set-url origin https://mirrors.ustc.edu.cn/homebrew-core.git
最后使用

brew update