PROPKA==3.1.0' distribution was not found

Hello all,

I installed propka 3.1 (https://github.com/jensengroup/propka-3.1) and I am unable to run the propka31 command. I get this message :

samuel@samuel-UX305CA:~$ propka31 '/home/samuel/Downloads/2jfz_monom_reFH.pdb'
Traceback (most recent call last):
File "/usr/local/bin/propka31", line 6, in
from pkg_resources import load_entry_point
File "/usr/lib/python2.7/dist-packages/pkg_resources/init.py", line 3088, in
@_call_aside
File "/usr/lib/python2.7/dist-packages/pkg_resources/init.py", line 3072, in _call_aside
f(*args, **kwargs)
File "/usr/lib/python2.7/dist-packages/pkg_resources/init.py", line 3101, in _initialize_master_working_set
working_set = WorkingSet._build_master()
File "/usr/lib/python2.7/dist-packages/pkg_resources/init.py", line 574, in _build_master
ws.require(requires)
File "/usr/lib/python2.7/dist-packages/pkg_resources/init.py", line 892, in require
needed = self.resolve(parse_requirements(requirements))
File "/usr/lib/python2.7/dist-packages/pkg_resources/init.py", line 778, in resolve
raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'PROPKA==3.1.0' distribution was not found and is required by the application

I'm new to gnu-linux so I don't know what to do to fix this issue. Any help would be very much appreciated.

Thanks in advance !

Samuel