fix typos

pointed out by nagachika.
http://d.hatena.ne.jp/nagachika/20130903/ruby_trunk_changes_42782_42812#r42799

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42821 b2dd03c8-39d4-4d8f-98ff-823fe69b080e