Fix scope resolution for MessageExts in Ruby

ruby/ext/google/protobuf_c/message.c

@@ -540,9 +540,9 @@ VALUE build_class_from_descriptor(Descriptor* desc) {
               get_def_obj(desc->msgdef));
   rb_define_alloc_func(klass, Message_alloc);
   rb_require("google/protobuf/message_exts");
-  rb_include_module(klass, rb_eval_string("Google::Protobuf::MessageExts"));
+  rb_include_module(klass, rb_eval_string("::Google::Protobuf::MessageExts"));
   rb_extend_object(
-      klass, rb_eval_string("Google::Protobuf::MessageExts::ClassMethods"));
+      klass, rb_eval_string("::Google::Protobuf::MessageExts::ClassMethods"));
 
   rb_define_method(klass, "method_missing",
                    Message_method_missing, -1);