Bump werkzeug from 0.9.4 to 0.15.3

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.9.4 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@0.9.4...0.15.3)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -1,6 +1,6 @@
 Babel==2.2.0
 PyYAML==3.11
-Werkzeug==0.9.4
+Werkzeug==0.15.3
 argparse==1.4.0
 ashes
 boltons