fix module_namespacing

lib/generators/decorator/decorator_generator.rb

@@ -23,6 +23,14 @@ module Rails
           "Draper::Decorator"
         end
       end
+
+      	
+      # Rails 3.0.X compatibility, stolen from https://github.com/jnunemaker/mongomapper/pull/385/files#L1R32
+      unless methods.include?(:module_namespacing)
+        def module_namespacing(&block)
+          yield if block
+        end
+      end
     end
   end
 end

lib/generators/decorator/templates/decorator.rb

@@ -1,5 +1,9 @@
-<% module_namespacing  do -%>
+<%- module_namespacing do -%>
+  <%- if parent_class_name.present? -%>
 class <%= class_name %>Decorator < <%= parent_class_name %>
+  <%- else -%>
+class <%= class_name %>
+  <%- end -%>
 
   # Accessing Helpers
   #   You can access any helper via a proxy