Pin to an older version of the docker package.

There's an issue with version 5.0.0, it requires six but it's missing from the package requirements. Pin to an older version until it's fixed.

Pin to an older version of the docker package.
c2e9c029 · nimrod · e5fb27b7 · c2e9c029
Commit c2e9c029 authored 3 years ago by nimrod
--- a/requirements.txt
+++ b/requirements.txt
-docker
+# Until https://github.com/docker/docker-py/issues/2842 and
+# https://github.com/docker/docker-py/issues/2807 are resolved.
+docker<5
 flask
 gunicorn