Bump werkzeug from 0.15.5 to 0.15.6

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.15.5 to 0.15.6.
- [Release notes](https://github.com/pallets/werkzeug/releases)
- [Changelog](https://github.com/pallets/werkzeug/blob/master/CHANGES.rst)
- [Commits](pallets/werkzeug@0.15.5...0.15.6)

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

requirements.txt

@@ -1,5 +1,5 @@
 Jinja2==2.10.1
-Werkzeug==0.15.5
+Werkzeug==0.15.6
 click==7.0
 gevent-websocket==0.10.1
 gevent==1.4.0