Ignore generators

especially since they are often ERB, not Ruby files even though they have
an .rb extension.

lib/brakeman/app_tree.rb

@@ -71,7 +71,7 @@ module Brakeman
     end
 
     def lib_paths
-      @lib_files ||= find_paths("lib")
+      @lib_files ||= find_paths("lib").reject { |path| path.include? "/generators/" }
     end
 
   private

test/apps/rails2/lib/generators/test_generator/templates/model.rb

+class <%= file_name.camelize %> < ActiveRecord::Base
+end