Custom helpers written in ES6 not fully compiled to ES5

[scssyworks]

This is a bug report:

Issue

Custom helpers not fully compiled to ES5 when used with handlebars-loader

Example:

import Handlebars from 'handlebars';
export default function () {
  return new Handlebars.SafeString(`<div>JS template string</div>`);
}

Output:

In output file template string is not converted to normal string.

Expected:

Helpers should be properly transpiled.