Bump flask from 2.0.3 to 2.1.1

Bumps [flask](https://github.com/pallets/flask) from 2.0.3 to 2.1.1.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/main/CHANGES.rst)
- [Commits](https://github.com/pallets/flask/compare/2.0.3...2.1.1)

---
updated-dependencies:
- dependency-name: flask
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

requirements.txt

@@ -1,7 +1,7 @@
 certifi==2021.10.8
 babel==2.9.1
 flask-babel==2.0.0
-flask==2.0.3
+flask==2.1.1
 jinja2==3.1.0
 lxml==4.8.0
 pygments==2.11.2