Merge pull request #339 from masamitsu-murase/initialize_module_mt_with_khash

Initialize mt of module with khash.

src/class.c

@@ -1065,6 +1065,7 @@ struct RClass *
 mrb_module_new(mrb_state *mrb)
 {
   struct RClass *m = (struct RClass*)mrb_obj_alloc(mrb, MRB_TT_MODULE, mrb->module_class);
+  m->mt = kh_init(mt, mrb);
 
   return m;
 }