Base parameters for Universal Transformer.

def universal_transformer_base():
  """Base parameters for Universal Transformer."""
  hparams = transformer.transformer_base()
  # To have a similar capacity to the transformer_base with 6 layers,
  # we need to increase the size of the UT's layer
  # since, in fact, UT has a single layer repeating multiple times.
  hparams.hidden_size = 1024
  hparams.filter_size = 4096
  hparams.num_heads = 16
  hparams.layer_prepostprocess_dropout = 0.3
  hparams = update_hparams_for_universal_transformer(hparams)
  return hparams