Update py to 1.5.4

[pyup-bot]

This PR updates py from 1.5.3 to 1.5.4.

Changelog

1.5.4

==================

- fix pytest-dev/pytest3451: don't make assumptions about fs case sensitivity
in ``make_numbered_dir``.

Links

• PyPI: https://pypi.org/project/py
• Changelog: https://pyup.io/changelogs/py/
• Repo: https://github.com/pytest-dev/py/issues
• Docs: http://py.readthedocs.io/

[pyup-bot]

Closing this in favor of #39