message: Fix bug in checker.check_node
  'tensors' is a repeated field in AttributeProto
diff: @@ -40,7 +40,6 @@ def check_node(node):
  for attr in node.attribute:
  if attr.HasField('t'):
  check_tensor(attr.t)
  - elif attr.HasField('tensors'):
  for tensor in attr.tensors:
  check_tensor(tensor)
  