Include es6 in your gulpfile.babel.js

gulpfile.babel.js

// npm install gulp-util --save

import gulpLoadPlugins from 'gulp-load-plugins';
import babelify from 'babelify';
import browserify from 'browserify';
import source from 'vinyl-source-stream';

var notifier = require('node-notifier');
// Standard handler
var standardHandler = function (err) {
  // Notification
  // var notifier = new notification();
  notifier.notify({ message: 'Error: ' + err.message });
  // Log to console
  $.util.log($.util.colors.red('Error'), err.message);
}

// Es6 browserify and babel
// enable module system
gulp.task('es6', () => {

  browserify({
    entries: './app/es6/main.js',
      debug: true
    })
    .transform(babelify)
    .on('error', standardHandler)
    .bundle()
    .on('error', standardHandler)
    .pipe(source('main.js'))
    .pipe(gulp.dest('./app/scripts/'));
});