make vue-loader to use postcss.config.js code example

Example 1: vue add sass

<!--
# Run this command in the root dir of your vue project:
npm i sass-loader node-sass style-loader
-->

<!-- And later in your vue component -->
<style lang="sass">
/* Your sass code */
</style>

Example 2: vue sass loader

<style lang="scss">
/* write SCSS here */
</style>