comment ruby version more specific.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@9979 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

mkconfig.rb

@@ -137,7 +137,7 @@ print <<EOS
     RbConfig::expand(val)
   end
 end
-Config = RbConfig # compatibility for ruby-1.8 and older.
+Config = RbConfig # compatibility for ruby-1.8.4 and older.
 CROSS_COMPILING = nil unless defined? CROSS_COMPILING
 EOS