Update requests to 2.18.1

[pyup-bot]

There's a new version of requests available.
You are currently using 2.17.3. I have updated it to 2.18.1

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

Changelog

2.18.1

+++++++++++++++++++

Bugfixes

• Fix an error in the packaging whereby the *.whl contained incorrect data that
  regressed the fix in v2.17.3.

2.18.0

+++++++++++++++++++

Improvements

• Response is now a context manager, so can be used directly in a with statement
  without first having to be wrapped by contextlib.closing().

Bugfixes

• Resolve installation failure if multiprocessing is not available
• Resolve tests crash if multiprocessing is not able to determine the number of CPU cores
• Resolve error swallowing in utils set_environ generator

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

Happy merging! 🤖