message: Update the docstring for "zero_output_for_mask" in RNN layer.
diff: @@ -266,6 +266,12 @@ class RNN(Layer):
  RNN calculation. However, most TensorFlow data is batch-major, so by
  default this function accepts input and emits output in batch-major
  form.
  + zero_output_for_mask: Boolean (default `False`).
  + Whether the output should use zeros for the masked timesteps. Note that
  + this field is only used when `return_sequences` is True and mask is
  + provided. It can useful if you want to reuse the raw output sequence of
  + the RNN without interference from the masked timesteps, eg, merging
  + bidirectional RNNs.
  Call arguments:
  inputs: Input tensor.
  