title: SweetAlert2 doesn't work on IE 11, Promise is not defined
body: <p>I'm using SweetAlert2 and on IE 11 throws exception:</p>
  
  <blockquote>
    <p>This package requires a Promise library, please include a shim to
    enable it in this browser (See:
    <a href="https://github.com/sweetalert2/sweetalert2/wiki/Migration-from-SweetAlert-to-SweetAlert2#1-ie-support" rel="nofollow noreferrer">https://github.com/sweetalert2/sweetalert2/wiki/Migration-from-SweetAlert-to-SweetAlert2#1-ie-support</a>)</p>
  </blockquote>
  
  <p>Because IE 11 doesn't support Promises and needs to be added manually.</p>
  
  <p>I'm using bluebird like so:</p>
  
  <pre><code>const Promise = require('bluebird');
  const Swal = require('sweetalert2');
  
  Swal.fire(...)
  ...
  </code></pre>
  
  <p>But still, sweetalert's check doesn't pass:</p>
  
  <pre><code>..
    if (typeof Promise === 'undefined') {
      error('This package requires a Promise library, please include a shim to enable it in this browser (See: https://github.com/sweetalert2/sweetalert2/wiki/Migration-from-SweetAlert-to-SweetAlert2#1-ie-support)');
    }
  ..
  </code></pre>
  
  <p>How to fix it? Thanks.</p>