Bump flask from 0.12.2 to 1.0 in /requirements

Bumps [flask](https://github.com/pallets/flask) from 0.12.2 to 1.0.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/master/CHANGES.rst)
- [Commits](pallets/flask@0.12.2...1.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/common.txt

@@ -3,7 +3,7 @@ bleach==2.0.0
 blinker==1.4
 click==6.7
 dominate==2.3.1
-Flask==0.12.2
+Flask==1.0
 Flask-Bootstrap==3.3.7.1
 Flask-HTTPAuth==3.2.3
 Flask-Login==0.4.0