io.c: fix typo
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56393 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
io.c: fix typo
[ruby-core:77550] [Bug ]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56393 b2dd03c8-39d4-4d8f-98ff-823fe69b080e