Update flask to 1.1.2

[pyup-bot]

This PR updates Flask from 1.1.1 to 1.1.2.

Changelog

1.1.2

-------------

Released 2020-04-03

-   Work around an issue when running the ``flask`` command with an
 external debugger on Windows. :issue:`3297`
-   The static route will not catch all URLs if the ``Flask``
 ``static_folder`` argument ends with a slash. :issue:`3452`

Links

• PyPI: https://pypi.org/project/flask
• Changelog: https://pyup.io/changelogs/flask/
• Homepage: https://palletsprojects.com/p/flask/