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] <[email protected]>

Author: dependabot[bot]

Diff for: requirements.txt

@@ -9,4 +9,4 @@ Jinja2==2.10
 MarkupSafe==1.0
 requests==2.18.4
 urllib3==1.22
-Werkzeug==0.14.1
+Werkzeug==0.15.3