Extract serialize? check into its own method

Author: benedikt

lib/userlist/push/serializer.rb

@@ -12,14 +12,18 @@ def serialize(resource)
         resource
       end
 
+      def serialize?(resource)
+        resource.push?
+      end
+
     private
 
       def serialize_resource(resource)
         return resource.identifier if serialized_resources.include?(resource)
 
         serialized_resources << resource
 
-        return unless resource.push?
+        return unless serialize?(resource)
 
         serialized = {}