Bump flask from 0.12.4 to 1.0 in /app

Bumps [flask](https://github.com/pallets/flask) from 0.12.4 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/0.12.4...1.0)

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

app/requirements.txt

@@ -8,7 +8,7 @@ Click==7.0
 CouchDB==1.2
 cryptography==2.4.2
 dominate==2.3.5
-Flask==0.12.4
+Flask==1.0
 flask-appconfig==0.11.1
 Flask-Bootstrap==3.3.7.1
 Flask-Cache==0.13.1