方式一：
npm install --save node-sass --registry=https://registry.npm.taobao.org --disturl=
https://npm.taobao.org/dist --sass-binary-site=
http://npm.taobao.org/mirrors/node-sass
方式二：
卸载node-sass sass-loader，重装
npm uninstall node-sass sass-loader
cnpm install node-sass sass-loader
可以先参考这位大佬https://segmentfault.com/a/1190000020993365?utm_source=tag-newest