解决homebrew无法更新软件问题

1. Error: Fetching /usr/local/Homebrew failed!

• 原因：homebrew-core文件夹有问题
• 解决方法：

git clone git://mirrors.ustc.edu.cn/homebrew-core.git/ /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core --depth=1
cd "$(brew --repo)"
git remote set-url origin https://mirrors.ustc.edu.cn/brew.git
cd "$(brew --repo)/Library/Taps/homebrew/homebrew-core" 
git remote set-url origin https://mirrors.ustc.edu.cn/homebrew-core.git
brew update
git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow

2.使用cu升级

brew tap buo/cask-upgrade
brew cu -f -a