gem install compass
如果安装不了，更换源试试
先移出
gem sources --remove https://rubygems.org/
再添加
gem source -a http://gems.ruby-china.com
然后再重新运行，就可以愉快的安装了。
gem install compass
如果遇到
You don't have write permissions for the /Library/Ruby/Gems/2.6.0 directory. 可以点此查看
