message: Updated python/demo.py to work with latest model changes
  We recently added vertex_definitions to the MorphableModel constructor, this broke that line in the Python demo script.
  As we use direct ibug-id to vertex-index mappings, we pass None here for the model's vertex definitions.
diff: @@ -11,8 +11,9 @@ def main():
  blendshapes = eos.morphablemodel.load_blendshapes("../share/expression_blendshapes_3448.bin")
  # Create a MorphableModel with expressions from the loaded neutral model and blendshapes:
  morphablemodel_with_expressions = eos.morphablemodel.MorphableModel(model.get_shape_model(), blendshapes,
  - eos.morphablemodel.PcaModel(),
  - model.get_texture_coordinates())
  + color_model=eos.morphablemodel.PcaModel(),
  + vertex_definitions=None,
  + texture_coordinates=model.get_texture_coordinates())
  landmark_mapper = eos.core.LandmarkMapper('../share/ibug_to_sfm.txt')
  edge_topology = eos.morphablemodel.load_edge_topology('../share/sfm_3448_edge_topology.json')
  contour_landmarks = eos.fitting.ContourLandmarks.load('../share/ibug_to_sfm.txt')
  