Bump flask from 0.10.1 to 1.0 in /demo-flask

Bumps [flask](https://github.com/pallets/flask) from 0.10.1 to 1.0.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/master/CHANGES.rst)
- [Commits](pallets/flask@0.10.1...1.0)

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

Author: dependabot[bot]

demo-flask/requirements.txt

@@ -1 +1 @@
-flask==0.10.1
+flask==1.0