Use require_relative to load rbconfig in default.mspec

* Otherwise it would load it twice.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58479 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/default.mspec

@@ -1,5 +1,5 @@
 # -*- ruby -*-
-load "./rbconfig.rb"
+require_relative "../rbconfig"
 load File.dirname(__FILE__) + '/rubyspec/default.mspec'
 OBJDIR = File.expand_path("spec/rubyspec/optional/capi/ext")
 class MSpecScript