如何安装Sass
https://www.sass.hk

sass基于Ruby语言开发而成，因此安装sass前需要安装Ruby。（注:mac下自带Ruby无需在安装Ruby!）

//1.删除原gem源
gem sources –remove https://rubygems.org/

//2.添加国内淘宝源
gem sources -a https://ruby.taobao.org/

//3.打印是否替换成功
gem sources -l

//4.更换成功后打印如下
*** CURRENT SOURCES ***
https://ruby.taobao.org/

//安装如下(如mac安装遇到权限问题需加 sudo gem install sass)
gem install sass
gem install compass

如果报错 You must add /O=Digital Signature Trust Co./CN=DST Root CA X3 to your local
sudo gem install -n /usr/local/bin sass
sudo gem install -n /usr/local/bin compass