illegal -> invalid.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@14386 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

bootstraptest/test_syntax.rb

@@ -624,7 +624,7 @@ assert_equal '2', %q{
   end
 }
 
-assert_match /illegal multibyte char/, %q{
+assert_match /invalid multibyte char/, %q{
   STDERR.reopen(STDOUT)
   eval("\"\xf0".force_encoding("utf-8"))
 }, '[ruby-dev:32429]'