1.常见问题
问题1：当执行npm run serve时，出现Failed to resolve loader: node-sass，You may need to install it
解决方法：
npm install node-sass@4.14.1
问题2：当执行npm run serve时，出现以下错误
Failed to resolve loader: sass-loader
You may need to install it
解决方法：
npm install sass-loader@8.0.2