fatal: unable to access 'https:/

解决：
// 执行下面这句命令，更换为中科院的镜像：
git clone git://mirrors.ustc.edu.cn/homebrew-core.git/ /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core --depth=1

// 把homebrew-core的镜像地址也设为中科院的国内镜像

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

// 更新
brew update