使用brew安装旧版本icu4c，icu4c 64.2

进入homebrew目录

cd $(brew --prefix)/Homebrew/Library/Taps/homebrew/homebrew-core/Formula

　　

查看git的提交记录

git log --follow icu4c.rb

　　

切换到64.2的提交

git checkout -b icu4c-64.2 896d1018c7a4906f2c3fa1386aaf283497db60a2

brew重新安装icu4c　

brew reinstall ./icu4c.rb