Bump werkzeug from 0.8.3 to 0.15.3

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.8.3 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@0.8.3...0.15.3)

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

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 Flask==0.9
 Jinja2==2.11.3
-Werkzeug==0.8.3
+Werkzeug==0.15.3
 argparse==1.2.1
 wsgiref==0.1.2