show foreign keys when run on rake task

lib/tasks/annotate_models.rake

@@ -17,6 +17,7 @@ task :annotate_models => :environment do
   options[:position_in_factory] = Annotate.fallback(ENV['position_in_factory'], ENV['position'])
   options[:position_in_test] = Annotate.fallback(ENV['position_in_test'], ENV['position'])
   options[:position_in_serializer] = Annotate.fallback(ENV['position_in_serializer'], ENV['position'])
+  options[:show_foreign_keys] = Annotate.true?(ENV['show_foreign_keys'])
   options[:show_indexes] = Annotate.true?(ENV['show_indexes'])
   options[:simple_indexes] = Annotate.true?(ENV['simple_indexes'])
   options[:model_dir] = ENV['model_dir'] ? ENV['model_dir'].split(',') : []