[Feature Request] 使用了postcss-px2rem插件，引入popup组件，报vux_modal.css路径错误

### Existing Component
是

### Component Name
Popup

### Description
解决方法：
vue-loader.config.js增加了两个配置
module.exports = {
loaders: utils.cssLoaders({
sourceMap: sourceMapEnabled,
extract: isProduction,
usePostCSS: true，//这里设置为true,否则vue引入css会报错
}),
postcss: [//postcss配置
require('postcss-px2rem')({remUnit: 37.5}),
],
cssSourceMap: sourceMapEnabled,
cacheBusting: config.dev.cacheBusting,
transformToRequire: {
video: ['src', 'poster'],
source: 'src',
img: 'src',
image: 'xlink:href'
}
}