Fix a typo [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61751 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

insns.def

@@ -5,7 +5,7 @@
   created at: 04/01/01 01:17:55 JST
 
   Copyright (C) 2004-2007 Koichi Sasada
-  Massive rewtite by @shyouhei in 2017.
+  Massive rewrite by @shyouhei in 2017.
  */
 
 /* Some comments about this file's contents: