Failure after upgrading to Ubuntu 18.04 LTS

[md5577]

Hello,

I've recently upgraded the Ubuntu system hosting the PatchServer from version 16.04 LTS to version 18.04 LTS. The service is now failing to start with the message:

$ sudo systemctl status patchserver.service

● patchserver.service - Patch Server daemon
   Loaded: loaded (/etc/systemd/system/patchserver.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Wed 2019-06-12 14:24:17 EDT; 20s ago
  Process: 22753 ExecStart=/usr/local/patchserver-venv/bin/gunicorn --pid /run/gunicorn/pid --config /opt/patchserver/config.py --log-level info --access-logfile /opt/patchserver/access.log wsgi (code=exited, status=1/FAILURE)
 Main PID: 22753 (code=exited, status=1/FAILURE)

Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]:     from gunicorn import util
Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]:   File "/usr/local/patchserver-venv/local/lib/python2.7/site-packages/gunicorn/util.py", line 12, in <module>
Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]:     import pkg_resources
Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]:   File "/usr/local/patchserver-venv/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 71, in <module>
Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]:     __import__('pkg_resources.extern.packaging.requirements')
Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]:   File "/usr/local/patchserver-venv/local/lib/python2.7/site-packages/pkg_resources/extern/__init__.py", line 60, in load_module
Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]:     "distribution.".format(**locals())
Jun 12 14:24:17 pnt-jamfpro1 gunicorn[22753]: ImportError: The 'packaging.requirements' package is required; normally this is bundled with this package so if you get this warning, consult the packager of your distribution.
Jun 12 14:24:17 pnt-jamfpro1 systemd[1]: patchserver.service: Main process exited, code=exited, status=1/FAILURE
Jun 12 14:24:17 pnt-jamfpro1 systemd[1]: patchserver.service: Failed with result 'exit-code'.

Any advise on how to fix this issue?
Thank you.