Bump flask from 0.12.4 to 1.0 in /manager

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](pallets/flask@0.12.4...1.0)

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

Author: dependabot[bot]

manager/requirements.txt

@@ -6,7 +6,7 @@ chardet==3.0.4
 click==6.7
 docker==3.3.0
 docker-pycreds==0.2.3
-Flask==0.12.4
+Flask==1.0
 future==0.16.0
 gitdb2==2.0.3
 GitPython==2.1.10