message: update arg doc for sigmoid_cross_entropy
  fixes
diff: @@ -676,8 +676,9 @@ def sigmoid_cross_entropy(
  `{0, 1}`.
  logits: Float `[batch_size, num_classes]` logits outputs of the network.
  weights: Optional `Tensor` whose rank is either 0, or the same rank as
  - `labels`, and must be broadcastable to `labels` (i.e., all dimensions must
  - be either `1`, or the same as the corresponding `losses` dimension).
  + `multi_class_labels`, and must be broadcastable to `multi_class_labels`
  + (i.e., all dimensions must be either `1`, or the same as the
  + corresponding `losses` dimension).
  label_smoothing: If greater than `0` then smooth the labels.
  scope: The scope for the operations performed in computing the loss.
  loss_collection: collection to which the loss will be added.
  