Merge pull request #4477 from shuujii/kernel-itself-should-not-be-a-module-function

`Kernel#itself` should not be a module function

mrbgems/mruby-object-ext/src/object.c

@@ -118,7 +118,8 @@ mrb_mruby_object_ext_gem_init(mrb_state* mrb)
   mrb_define_method(mrb, n, "to_f", nil_to_f,       MRB_ARGS_NONE());
 #endif
   mrb_define_method(mrb, n, "to_i", nil_to_i,       MRB_ARGS_NONE());
-  mrb_define_module_function(mrb, mrb->kernel_module, "itself", mrb_f_itself, MRB_ARGS_NONE());
+
+  mrb_define_method(mrb, mrb->kernel_module, "itself", mrb_f_itself, MRB_ARGS_NONE());
 
   mrb_define_method(mrb, mrb_class_get(mrb, "BasicObject"), "instance_exec", mrb_obj_instance_exec, MRB_ARGS_ANY() | MRB_ARGS_BLOCK());
 }