Bump flask from 1.0.3 to 1.1.1 (#124)

Bumps [flask](https://github.com/pallets/flask) from 1.0.3 to 1.1.1.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/flask/compare/1.0.3...1.1.1

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements.txt

 backports.tempfile==1.0
-Flask==1.0.3
+Flask==1.1.1
 gevent==1.4.0
 gunicorn==19.9.0
 futures