proc vs. lambda ambiguity in 1.8.7 and 1.9.2

It seems lambdas have to have the correct number of arguments while procs don't - this was not happening in 1.8.7

Fixes #2

init.rb

@@ -111,5 +111,5 @@ Redmine::Plugin.register :backlogs do
        :caption => :project_module_backlogs,
        :before => :calendar,
        :param => :project_id,
-       :if => lambda { not(User.current.respond_to?(:impaired?) and User.current.impaired?) }
+       :if => proc { not(User.current.respond_to?(:impaired?) and User.current.impaired?) }
 end