[Security] 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. **This update includes a security fix.**
- [Release notes](https://github.com/pallets/werkzeug/releases)
- [Changelog](https://github.com/pallets/werkzeug/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/werkzeug/compare/0.14.1...0.15.3

)

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

requirements-dev.txt

@@ -6,5 +6,5 @@ Faker==1.0.8  # Pinning to avoid API changes to pydecimal in 0.x - could go high
 flake8==3.7.9
 responses==0.10.6
 stellar==0.4.5
-wagtail-factories==1.1.0
+wagtail-factories==2.0.0
 Werkzeug==0.15.3