Update modernie property provider to recognize IE11 on WP 8.1 Update (#14376)

Change-Id: I8df8260bf875dd2a3cf974885bde8b473f4951a5

client/src/com/vaadin/Vaadin.gwt.xml

     <property-provider name="modernie"><![CDATA[
       {
         var ua = $wnd.navigator.userAgent;
-        if (ua.indexOf('IE') == -1 && ua.indexOf('Trident') != -1) { return 'yes'; }
+        if (ua.indexOf('MSIE') == -1 && ua.indexOf('Trident') != -1) { return 'yes'; }
         return 'none';
       }
     ]]></property-provider>