Fix flake8 warning.
Fix flake8 warning.

See [issue 110 in flake8][flakeissue], but OSError and IOError were only
different in python2, and are the same in python3. Hence, only one of
them is needed and flake8 will be unhappy if both are listed.

[flakeissue]: https://github.com/PyCQA/flake8-bugbear/issues/110

hobarrera/todoman,pimutils/todoman