BUGFIX: Neos.NodeTypes:Menu has no default class attribute

This fixes a previous breaking change where "Menu" node-type is not
getting a default class attribute rendered for instance 'neos-nodetypes-menu'
where a website's stylesheet is relying on this CSS class

Neos.NodeTypes.Navigation/Resources/Private/Fusion/Root.fusion

@@ -12,6 +12,8 @@ prototype(Neos.NodeTypes.Navigation:Navigation) < prototype(Neos.Neos:Menu) {
   maximumLevels = ${q(node).property('maximumLevels')}
   maximumLevels.@process.1 = ${String.toInteger(value)}
 
+  attributes.class.@process < prototype(Neos.Neos:Content).attributes.class.@process
+
   active.attributes = Neos.Fusion:Attributes {
     class = 'active'
   }