NPM国内镜像
http://npm.hacknodejs.com/
http://registry.npmjs.vitecho.com/
https://registry.npm.taobao.org
永久使用镜像命令:
npm config set registry https://registry.npm.taobao.org
临时使用镜像命令: npm --registry "http://npm.hacknodejs.com/" install underscore