update doc.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39554 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-03-03

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39555 b2dd03c8-39d4-4d8f-98ff-823fe69b080e