Bump flask from 0.10.1 to 1.0 in /beginner/flask-app

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](https://github.com/pallets/flask/compare/0.10.1...1.0)

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

beginner/flask-app/requirements.txt

@@ -1 +1 @@
-Flask==0.10.1
+Flask==1.0