PEP 540: Correct sys.output to sys.stdout (#4122)

Author: PallHaraldsson

peps/pep-0540.rst

@@ -259,7 +259,7 @@ The "Legacy Windows FS encoding" is enabled by the
 ``PYTHONLEGACYWINDOWSFSENCODING`` environment variable.
 
 If stdin and/or stdout is redirected to a pipe, ``sys.stdin`` and/or
-``sys.output`` uses ``mbcs`` encoding by default rather than UTF-8.
+``sys.stdout`` uses ``mbcs`` encoding by default rather than UTF-8.
 But in UTF-8 Mode, ``sys.stdin`` and ``sys.stdout`` always use the UTF-8
 encoding.