Update requests-mock to 1.9.0

[pyup-bot]

This PR updates requests-mock from 1.5.0 to 1.9.0.

Changelog

1.8.0

Solidifies the behaviour of nested mocking and the real_http variable.

1.7.0

Releasing a few pull-requests that people will find useful. 

Includes fixes for 93 and 106. These should be inconsequential for most people.

Links

• PyPI: https://pypi.org/project/requests-mock
• Changelog: https://pyup.io/changelogs/requests-mock/
• Docs: https://requests-mock.readthedocs.io/

[pyup-bot]

Closing this in favor of #397