Laravel 5.3 Elixir Webpack - does not transpile Object.assign to EcmaScript 2015

Question

I'm using Laravel 5.3 and utilizing the bootstrap app.js file provided by Laravel itself.

This is how my gulpfile.js looks like:

const elixir = require('laravel-elixir');

require("babel-polyfill");
require('laravel-elixir-vue-2');

/*
 |--------------------------------------------------------------------------
 | Elixir Asset Management
 |--------------------------------------------------------------------------
 |
 | Elixir provides a clean, fluent API for defining some basic Gulp tasks
 | for your Laravel application. By default, we are compiling the Sass
 | file for your application as well as publishing vendor resources.
 |
 */

elixir((mix) => {
    mix
        .webpack(
            './resources/assets/SPA/app.js',
            './public/js/app.js');
});

When I use IE 11 I get the following error (in the console):

"Object doesn't support property or method 'assign'

I wonder if is there any way to solve this? I've tried to use babel-transpile but that, unfortunately, didn't work - maybe because I've misused it.

Any help would be highly appreicated!