Laravel mix keep creating minified file

Question

When I use laravel mix with these commands npm run dev or npm run watch, they still create a minified file for the Highcharts library. How can I get the unminified version at least in dev ?

Here my files

webpack.mix.js

let mix = require('laravel-mix');
mix.js('resources/assets/js/app.js', 'public/js');
mix.autoload({  // or Mix.autoload() ?
    'jquery': ['$', 'window.jQuery', 'jQuery']
});

app.js

...
import Highcharts from 'highcharts/highcharts';
// import Highcharts from 'highcharts/highcharts.src.js'; // not working
// import Highcharts from 'highcharts/js/highcharts.src.js'; // not working
import HighchartsMore from 'highcharts/highcharts-more.src.js'; // works
HighchartsMore(Highcharts);
...
import HighchartsVue from 'highcharts-vue';
Vue.use(HighchartsVue);