foundation-sites: GetYoDigits() causing IE to fail 'invalid character'

Expected Behavior

IE 11 should load JavaScript.

Current Behavior

IE 11 script error invalid character in app.js (character 125) of the following line

return Math.round((Math.pow(36, length + 1) - Math.random() * Math.pow(36, length))).toString(36).slice(1) + (namespace ? `-${namespace}` : '');

Possible Solution

There needs to be a transpile step

How to reproduce:

1. Running a Foundation for sites using app.js open in IE 11

Context

This is haulting my development team from releasing products

Your Environment

• Foundation version(s) used: 6.4.3
• Browser(s) name and version(s): IE 11
• Operating System and version (desktop or mobile): Desktop

Checklist (all required):

• I have read and follow the CONTRIBUTING document.
• This is a bug report or a feature request.
• There are no other issues similar to this one.
• The issue title is descriptive.
• The template is fully and correctly filled.