message: Add one more reference. The last modified date tripped me up earlier.
  Relates to
diff: @@ -516,13 +516,13 @@ def swish(features):
  # pylint: disable=g-doc-args
  """Computes the SiLU or Swish activation function: `x * sigmoid(x)`.
  - The SiLU activation was introduced in "Sigmoid-Weighted Linear Units for
  - Neural Network Function Approximation in Reinforcement Learning" (Elfwing et
  - al. 2017) https://arxiv.org/abs/1702.03118
  -
  - and was independently discovered (and called swish) in "Searching for
  - Activation Functions" (Ramachandran et al. 2017)
  - https://arxiv.org/abs/1710.05941
  + The SiLU activation function was introduced in "Gaussian Error Linear Units
  + (GELUs)" [Hendrycks et al. 2016](https://arxiv.org/abs/1606.08415) and
  + "Sigmoid-Weighted Linear Units for Neural Network Function Approximation in
  + Reinforcement Learning"
  + [Elfwing et al. 2017](https://arxiv.org/abs/1702.03118) and was independently
  + discovered (and called swish) in "Searching for Activation Functions"
  + [Ramachandran et al. 2017](https://arxiv.org/abs/1710.05941)
  Args:
  features: A `Tensor` representing preactivation values.
  