Bump werkzeug from 0.15.1 to 0.15.3

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.15.1 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@0.15.1...0.15.3) Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 Flask==1.0.2
-werkzeug==0.15.1
+werkzeug==0.15.3
 
 # Application server for both development and production.
 gunicorn==19.7.0