message: fix a bug of model_to_dot()
diff: @@ -120,7 +120,7 @@ def model_to_dot(model, show_shapes=False, show_layer_names=True, rankdir='TB'):
  layer_id = str(id(layer))
  for i, node in enumerate(layer._inbound_nodes): # pylint: disable=protected-access
  node_key = layer.name + '_ib-' + str(i)
  - if node_key in model.container_nodes:
  + if node_key in model._network_nodes: # pylint: disable=protected-access
  for inbound_layer in node.inbound_layers:
  inbound_layer_id = str(id(inbound_layer))
  layer_id = str(id(layer))
  