Small model for tpu cifar 10.

def imagetransformer_b10l_4h_big_uncond_dr03_tpu():
  """Small model for tpu cifar 10."""
  hparams = imagetransformer_bas8l_8h_big_uncond_dr03_imgnet()
  update_hparams_for_tpu(hparams)
  hparams.batch_size = 4
  hparams.num_heads = 4   # heads are expensive on tpu
  hparams.num_decoder_layers = 10
  hparams.block_length = 128
  hparams.hidden_size = 512
  hparams.filter_size = 1024
  hparams.learning_rate = 0.2
  hparams.layer_preprocess_sequence = "none"
  hparams.layer_postprocess_sequence = "dan"
  return hparams