Update decorator to 5.0.8

[pyup-bot]

This PR updates decorator from 4.4.2 to 5.0.8.

Changelog

5.0.8

Made the decorator module more robust when decorating builtin functions
lacking dunder attributes, like `dict.__setitem__`.

5.0.7

The decorator module was not passing correctly the defaults inside the
`*args` tuple, thanks to Dan Shult for the fix. Also fixed some mispellings
in the documentation and integrated codespell in the CI, thanks to 
Christian Clauss.

5.0.6

The decorator module was not copying the __module__ attribute anymore. Thanks to
Nikolay Markov for the notice.

5.0.5

Dropped support for Python < 3.5 with a substantial simplification of
the code base (now building a decorator does not require calling "exec").
Added a way to mimic functools.wraps-generated decorators.
Ported the Continuous Integration from Travis to GitHub.

Links

• PyPI: https://pypi.org/project/decorator
• Changelog: https://pyup.io/changelogs/decorator/
• Repo: https://github.com/micheles/decorator

[pyup-bot]

Closing this in favor of #759