cd /usr/local
git remote set-url origin git://mirrors.tuna.tsinghua.edu.cn/homebrew.git
brew update
#如果速度还是很慢，可以尝试以下操作，然后重试update
cd ~/tmp
git clone git://mirrors.tuna.tsinghua.edu.cn/homebrew.git
rm -rf /usr/local/.git
rm -rf /usr/local/Library
cp -R homebrew/.git /usr/local/
cp -R homebrew/Library /usr/local/
http://heepo.github.io/%E5%B7%A5%E5%85%B7/2015/08/05/Homebrew-Mirror-Links.html [Homebrew镜像源]
