Update attribute_restrictions.py (#715)

Author: yuji38kwmt

annofabapi/util/attribute_restrictions.py

@@ -7,7 +7,7 @@
     .. code-block:: python
 
         >>> import annofabapi
-        >>> from annofabapi.util.annotation_specs import AnnotationSpecsAccessor
+        >>> from annofabapi.util.attribute_restrictions import AttributeFactory
         >>> service = annofabapi.build()
         >>> annotation_specs, _ = service.api.get_annotation_specs("prj1", query_params={"v": "3"})
         >>> fac = AttributeFactory(annotation_specs)