fix a typo [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50952 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: znz

ChangeLog

@@ -4,7 +4,7 @@ Thu Jun 18 18:24:12 2015  Eric Wong  <e@80x24.org>
 
 Thu Jun 18 17:59:06 2015  Koichi Sasada  <ko1@atdot.net>
 
-	* vm.c (rb_vm_control_frame_id_and_class): remove usless codes.
+	* vm.c (rb_vm_control_frame_id_and_class): remove useless codes.
 	  `me' knows ID and owner class.
 
 Thu Jun 18 16:58:35 2015  Koichi Sasada  <ko1@atdot.net>