Bump validators from 0.12.5 to 0.12.6 in /core/admin

Bumps [validators](https://github.com/kvesteri/validators) from 0.12.5 to 0.12.6.
- [Release notes](https://github.com/kvesteri/validators/releases)
- [Changelog](https://github.com/kvesteri/validators/blob/master/CHANGES.rst)
- [Commits](https://github.com/kvesteri/validators/commits)

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

core/admin/requirements-prod.txt

@@ -44,7 +44,7 @@ SQLAlchemy==1.3.3
 srslib==0.1.4
 tabulate==0.8.3
 tenacity==5.0.4
-validators==0.12.5
+validators==0.12.6
 visitor==0.1.3
 Werkzeug==0.15.3
 WTForms==2.2.1