Best config for 2.90 bits/dim on CIFAR10 using cross entropy.

def imagetransformer_cifar10_base():
  """Best config for 2.90 bits/dim on CIFAR10 using cross entropy."""
  hparams = image_transformer_base()
  hparams.batch_size = 4
  hparams.num_heads = 4
  hparams.num_decoder_layers = 12
  hparams.block_length = 256
  hparams.hidden_size = 512
  hparams.filter_size = 2048
  hparams.learning_rate = 0.5
  hparams.learning_rate_warmup_steps = 4000
  hparams.layer_preprocess_sequence = "none"
  hparams.layer_postprocess_sequence = "dan"
  hparams.layer_prepostprocess_dropout = 0.3
  hparams.unconditional = True
  return hparams