_asdict returns OrderedDict in 3.1 and up (#1690)

Author: Sterbic

stdlib/3/typing.pyi

@@ -520,7 +520,10 @@ class NamedTuple(tuple):
     @classmethod
     def _make(cls, iterable: Iterable[Any]) -> NamedTuple: ...
 
-    def _asdict(self) -> dict: ...
+    if sys.version_info >= (3, 1):
+        def _asdict(self) -> collections.OrderedDict[str, Any]: ...
+    else:
+        def _asdict(self) -> Dict[str, Any]: ...
     def _replace(self, **kwargs: Any) -> NamedTuple: ...
 
 def NewType(name: str, tp: Type[_T]) -> Type[_T]: ...