Bump werkzeug from 0.14.1 to 0.15.3

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.14.1 to 0.15.3.
- [Release notes](https://github.com/pallets/werkzeug/releases)
- [Changelog](https://github.com/pallets/werkzeug/blob/master/CHANGES.rst)
- [Commits](pallets/werkzeug@0.14.1...0.15.3)

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

requirements.txt

@@ -13,4 +13,4 @@ pytz==2018.5
 requests==2.22.0
 six==1.11.0
 urllib3==1.24.2
-Werkzeug==0.14.1
+Werkzeug==0.15.3