message: Add polyfill in html for better support in IE11
diff: <html>
  <head>
  <title>Botkit Anywhere</title>
  + <script src="https://cdn.polyfill.io/v3/polyfill.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/handlebars.js/4.0.10/handlebars.min.js"></script>
  <script src="https://cdn.rawgit.com/showdownjs/showdown/1.7.4/dist/showdown.min.js"></script>
  <link rel="stylesheet" href="/css/styles.css" />
  