Add newline before return

Co-authored-by: Olle Jonsson <olle.jonsson@gmail.com>

Author: zzak

lib/rdoc/task.rb

@@ -261,6 +261,7 @@ def define
         $stderr.puts "rdoc #{args.join ' '}" if Rake.application.options.trace
       end
     end
+
     self
   end