Fix to modeshape-cdi demo for Modeshape 3.7.1

[mdzmura]

This demo was giving an EL error in main.xhtml which I traced to this statement:

       <h:panelGrid columns="1" border="1" rendered="#{!cdiController.children.isEmpty()}">

I changed it to this to make it work:

        <h:panelGrid columns="1" border="1" rendered="#{not empty cdiController.children}">

-Mark