update elements and fix some bugs

lib/src/iron-a11y-announcer/iron-a11y-announcer.html

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 @license
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 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
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@@ skipping 36 matching lines @@
 <dom-module id="iron-a11y-announcer">
   <style>
     :host {
       display: inline-block;
       position: fixed;
       clip: rect(0px,0px,0px,0px);
     }
   </style>
 
   <template>
-    <span aria-live$="[[mode]]">[[_text]]</span>
+    <div aria-live$="[[mode]]">[[_text]]</div>
   </template>
 
   <script>
 
     (function() {
       'use strict';
 
       Polymer.IronA11yAnnouncer = Polymer({
         is: 'iron-a11y-announcer',
 
@@ skipping 48 matching lines @@
         if (!Polymer.IronA11yAnnouncer.instance) {
           Polymer.IronA11yAnnouncer.instance = document.createElement('iron-a11y-announcer');
         }
 
         document.body.appendChild(Polymer.IronA11yAnnouncer.instance);
       };
     })();
 
   </script>
 </dom-module>