insns.def: fix typo

* insns.def (defineclass): fix typo in the instruction comment.
  [fix GH-618]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46149 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-05-27

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46150 b2dd03c8-39d4-4d8f-98ff-823fe69b080e