Bump werkzeug from 0.12.2 to 0.15.3

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.12.2 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@0.12.2...0.15.3)

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

Author: dependabot[bot]

requirements.txt

@@ -3,7 +3,7 @@ Flask==0.12.2
 itsdangerous==0.24
 Jinja2==2.9.6
 MarkupSafe==1.0
-Werkzeug==0.12.2
+Werkzeug==0.15.3
 PyJWT==1.7.1
 boto3==1.9.145
 simplejson==3.16.0