old_contents: 
  module.exports = {
    entries: {
      application: '~app/assets/my_app/index.js',
    },
  };
  
new_contents: 
  function haulerConfigFactory(env) {
    return {
      entries: {
        application: '~app/assets/my_app/index.js',
      },
    };
  }
  
  module.exports = haulerConfigFactory;
  
subject: change hauler config to factory