Bump werkzeug from 0.14.1 to 0.15.3 in /src/loadgenerator

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] <support@github.com>

src/loadgenerator/requirements.txt

@@ -20,4 +20,4 @@ pyzmq==17.0.0             # via locustio
 requests==2.21.0          # via locustio
 six==1.12.0               # via locustio
 urllib3==1.24.2           # via requests
-werkzeug==0.14.1          # via flask
+werkzeug==0.15.3          # via flask