Fix tests

Author: ddfisher

stdlib/3/io.pyi

@@ -90,7 +90,7 @@ class BytesIO(BinaryIO):
 
     def __iter__(self) -> Iterator[bytes]: ...
     def __enter__(self) -> 'BytesIO': ...
-    def __exit__(self, type, value, traceback) -> bool: ...
+    def __exit__(self, t: type = None, value: BaseException = None, traceback: Any = None) -> bool: ...
 
 class StringIO(TextIO):
     def __init__(self, initial_value: str = ...,
@@ -117,7 +117,7 @@ class StringIO(TextIO):
 
     def __iter__(self) -> Iterator[str]: ...
     def __enter__(self) -> 'StringIO': ...
-    def __exit__(self, type, value, traceback) -> bool: ...
+    def __exit__(self, t: type = None, value: BaseException = None, traceback: Any = None) -> bool: ...
 
 class TextIOWrapper(TextIO):
     # TODO: This is actually a base class of _io._TextIOBase.
@@ -147,4 +147,4 @@ class TextIOWrapper(TextIO):
 
     def __iter__(self) -> Iterator[str]: ...
     def __enter__(self) -> StringIO: ...
-    def __exit__(self, type, value, traceback) -> bool: ...
+    def __exit__(self, t: type = None, value: BaseException = None, traceback: Any = None) -> bool: ...