Fix signature of Connection.iterdump() (#3843)

stdlib/2and3/sqlite3/dbapi2.pyi

@@ -3,7 +3,7 @@
 
 import os
 import sys
-from typing import Any, Callable, Iterable, Iterator, List, Optional, Text, Tuple, Type, TypeVar, Union
+from typing import Any, Callable, Generator, Iterable, Iterator, List, Optional, Text, Tuple, Type, TypeVar, Union
 from datetime import date, time, datetime
 
 _T = TypeVar('_T')
@@ -139,7 +139,7 @@ class Connection(object):
     def executemany(self, sql: str, seq_of_parameters: Iterable[Iterable[Any]]) -> Cursor: ...
     def executescript(self, sql_script: Union[bytes, Text]) -> Cursor: ...
     def interrupt(self, *args, **kwargs) -> None: ...
-    def iterdump(self, *args, **kwargs) -> None: ...
+    def iterdump(self, *args, **kwargs) -> Generator[str, None, None]: ...
     def rollback(self, *args, **kwargs) -> None: ...
     # TODO: set_authorizer(authorzer_callback)
     # see https://docs.python.org/2/library/sqlite3.html#sqlite3.Connection.set_authorizer