version conflict with PyYAML (3.11 vs 3.12)

[ochriste]

with the camptocamp/tilecloud-chain image

root@84dbefe842de:/project# generate_tiles --help
Traceback (most recent call last):
  File "/usr/local/bin/generate_tiles", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2991, in <module>
    @_call_aside
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2977, in _call_aside
    f(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 3004, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 664, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 677, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 861, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.ContextualVersionConflict: (PyYAML 3.12 (/usr/local/lib/python2.7/dist-packages), Requirement.parse('PyYAML==3.11'), set(['pykwalify']))