Base parameters for Transformer model.

def transformer_base_v3():
  """Base parameters for Transformer model."""
  # Update parameters here, then occasionally cut a versioned set, e.g.
  # transformer_base_v2.
  hparams = transformer_base_v2()
  hparams.optimizer_adam_beta2 = 0.997
  # New way of specifying learning rate schedule.
  # Equivalent to previous version.
  hparams.learning_rate_schedule = (
      "constant*linear_warmup*rsqrt_decay*rsqrt_hidden_size")
  hparams.learning_rate_constant = 2.0
  return hparams