cd $(brew --prefix)/Homebrew/Library/Taps/homebrew/homebrew-core/Formula
git log --follow icu4c.rb
git checkout -b icu4c-66.1 22fb699a417093cd1440857134c530f1e3794f7d
brew reinstall ./icu4c.rb
如果已安装，直接切换即可
/usr/local/Cellar/icu4c/66.1
/usr/local/opt/icu4c ->/usr/local/Cellar/icu4c/66.1
brew info icu4c 查看icu4c安装在了哪里
brew switch icu4c 66.1 <version>，切换到安装的版本
