Add 'closing' to 2.7 contextlib stubs (same as for 3).

stdlib/2.7/contextlib.pyi

@@ -2,7 +2,14 @@
 
 # NOTE: These are incomplete!
 
-from typing import Any
+from typing import Any, TypeVar, Generic
 
 # TODO more precise type?
 def contextmanager(func: Any) -> Any: ...
+
+_T = TypeVar('_T')
+
+class closing(Generic[_T]):
+    def __init__(self, thing: _T) -> None: ...
+    def __enter__(self) -> _T: ...
+    def __exit__(self, *exc_info) -> None: ...