[5458710] Added koans about to_str

koans/path_to_enlightenment.rb

@@ -31,6 +31,7 @@ require 'about_scope'
 require 'about_class_methods'
 require 'about_message_passing'
 require 'about_proxy_object_project'
+require 'about_to_str'
 in_ruby_version("jruby") do
   require 'about_java_interop'
 end