Please download the updated messager plugin from
http://www.jeasyui.com/easyui/plugins/jquery.messager.js and include it to your page.
<script type="text/javascript" src="../../jquery.easyui.min.js"></script>
<script type="text/javascript" src="http://www.jeasyui.com/easyui/plugins/jquery.messager.js"></script>
<script type="text/javascript">
$(function(){
$.messager.show({
title:'My Title',
msg:'Message will be closed after 4 seconds.',
showType:'show',
modal:true
});
})
</script>