update samples

samples/server/petstore/python-flask/openapi_server/models/base_model_.py

@@ -8,14 +8,14 @@ from openapi_server import util
 T = typing.TypeVar('T')
 
 
-class Model(object):
+class Model():
     # openapiTypes: The key is attribute name and the
     # value is attribute type.
-    openapi_types = {}
+    openapi_types: typing.Dict[str, type] = {}
 
     # attributeMap: The key is attribute name and the
     # value is json key in definition.
-    attribute_map = {}
+    attribute_map: typing.Dict[str, str] = {}
 
     @classmethod
     def from_dict(cls: typing.Type[T], dikt) -> T: