drop enum34 requirement for python3

[TomasTomecek]

Traceback (most recent call last):
  File "/bin/colin", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3088, in <module>                                                                                 
    @_call_aside
  File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3072, in _call_aside                                                                              
    f(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3101, in _initialize_master_working_set                                                           
    working_set = WorkingSet._build_master()
  File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 574, in _build_master                                                                             
    ws.require(__requires__)
  File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 892, in require                                                                                   
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 778, in resolve                                                                                   
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'enum34' distribution was not found and is required by conu