A couple fixes to the io stubs. (#1811)

1. The 'name' argument to FileIO.init can be either a string or an integer: https://docs.python.org/2/library/io.html#io.FileIO
2. An mmap.mmap object can be used in most places that a bytearray can: https://docs.python.org/3.5/library/mmap.html

stdlib/3/http/client.pyi

@@ -89,7 +89,6 @@ if sys.version_info >= (3, 5):
         def __init__(self, sock: socket, debuglevel: int = ...,
                      method: Optional[str] = ..., url: Optional[str] = ...) -> None: ...
         def read(self, amt: Optional[int] = ...) -> bytes: ...
-        def readinto(self, b: bytearray) -> int: ...
         @overload
         def getheader(self, name: str) -> Optional[str]: ...
         @overload