[docs] [issue37730] NotImplemented is used instead of NotImplementedError in docs

[Serhiy Storchaka]

Change by Serhiy Storchaka <storchaka+cpython at gmail.com>:


----------
pull_requests: +14848
pull_request: https://github.com/python/cpython/pull/15106

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37730>
_______________________________________