Fix recursive type test

Author: misakwa

tests/test_hook.py

@@ -135,5 +135,6 @@ def test_load_slots():
     rec = thriftpy.load('parser-cases/recursive_union.thrift', use_slots=True)
     rec_slots = rec.Dynamic.__slots__
     assert rec_slots == ['boolean', 'integer', 'doubl', 'str', 'arr', 'object']
+    dyn = rec.Dynamic()
     with pytest.raises(AttributeError):
-        rec.Dynamic.attr_not_exist = "shouldn't work"
+        dyn.attr_not_exist = "shouldn't work"