【参考： https://blog.csdn.net/youshaoduo/article/details/89228454】
cd $(brew --prefix)/Homebrew/Library/Taps/homebrew/homebrew-core/Formula
git log --follow icu4c.rb
git checkout -b icu4c-63.1 bc0c97952453ff6afc146aa3a706e9902aba4300
brew reinstall ./icu4c.rb
如果已安装，直接切换即可
/usr/local/Cellar/icu4c/62.1
/usr/local/opt/icu4c -> ../Cellar/icu4c/62.1
brew info icu4c 查看icu4c安装在了哪里
brew switch icu4c 63.1 <version>，切换到安装的版本
"cxx11" is not a recognized standard
Removing need :cxx11 from /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/php@7.1.rb
(https://github.com/caskformula/homebrew-caskformula/issues/74)
无效的！！！1