update werkzeug to 0.15.3 or later due to CVE-2019-14806

[redshiftzero]

Description

We should update werkzeug to version 0.15.3 or later due to CVE-2019-14806. CVE-2019-14806 is a bug in the randomness used for generating the pin in the debugger in docker (same pin across all containers!). We only use docker in a development environment, and we also only use the debugger in a development environment, so this is dev only. Nevertheless we should update to a version of this dependency that does not have a known CVE.