Update decorator to 4.2.0

[pyup-bot]

There's a new version of decorator available.
You are currently using 4.0.10. I have updated it to 4.2.0

These links might come in handy: PyPI | Changelog | Repo

Changelog

4.2.0

Added a facility to define families of decorators (aka decorators with
arguments) as requested by several users. Accepted a pylint patch by
David Allouche.

4.1.2

Made it possible to define decorators converting coroutines into regular
functions, as requested by Itaï Ben Yaacov.

4.1.1

Changed the documentation build system to sphinx and uploaded the docs
on readthedocs.org.

4.1.0

Support for Python 3.5 coroutines defined with async def, thanks to
Victor-Nicolae Savu who raised the issue of iscoroutinefunction not
giving the right answer for coroutines decorated with the decorator module.

4.0.11

Small improvements to the documentation and tested with Python 3.6

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[pyup-bot]

Closing this in favor of #197