Issue running run_transfo_xl.py
Author: korymath
Pull request: no

Run code: 
```
python run_transfo_xl.py --work_dir ../log
```

Output
```
07/16/2019 18:01:46 - INFO - __main__ -   device: cuda
07/16/2019 18:01:46 - INFO - pytorch_transformers.tokenization_utils -   loading file https://s3.amazonaws.com/models.huggingface.co/bert/transfo-xl-wt103-vocab.bin from cache at /home/korymathewson/.cache/torch/pytorch_transformers/b24cb708726fd43cbf1a382da9ed3908263e4fb8a156f9e0a4f45b7540c69caa.a6a9c41b856e5c31c9f125dd6a7ed4b833fbcefda148b627871d4171b25cffd1
07/16/2019 18:01:46 - INFO - pytorch_transformers.tokenization_utils -   loading file https://s3.amazonaws.com/models.huggingface.co/bert/transfo-xl-wt103-vocab.bin from cache at /home/korymathewson/.cache/torch/pytorch_transformers/b24cb708726fd43cbf1a382da9ed3908263e4fb8a156f9e0a4f45b7540c69caa.a6a9c41b856e5c31c9f125dd6a7ed4b833fbcefda148b627871d4171b25cffd1
07/16/2019 18:01:47 - INFO - pytorch_transformers.tokenization_transfo_xl -   loading corpus file https://s3.amazonaws.com/models.huggingface.co/bert/transfo-xl-wt103-corpus.bin from cache at /home/korymathewson/.cache/torch/pytorch_transformers/b927918d674805742f3febcd807b375d5819f40410b83d09e3c0fb8344394216.a7d11b2fa856afe836727fbd95638053f056c4a3ac571d7800faed25ce81a4e1
07/16/2019 18:01:53 - INFO - pytorch_transformers.modeling_utils -   loading configuration file https://s3.amazonaws.com/models.huggingface.co/bert/transfo-xl-wt103-config.json from cache at /home/korymathewson/.cache/torch/pytorch_transformers/a6dfd6a3896b3ae4c1a3c5f26ff1f1827c26c15b679de9212a04060eaf1237df.aef76fb1064c932cd6a2a2be3f23ebbfa5f9b6e29e8e87b571c45b4a5d5d1b90
07/16/2019 18:01:53 - INFO - pytorch_transformers.modeling_utils -   Model config {
  "adaptive": true,
  "attn_type": 0,
  "clamp_len": 1000,
  "cutoffs": [
    20000,
    40000,
    200000
  ],
  "d_embed": 1024,
  "d_head": 64,
  "d_inner": 4096,
  "d_model": 1024,
  "div_val": 4,
  "dropatt": 0.0,
  "dropout": 0.1,
  "ext_len": 0,
  "finetuning_task": null,
  "init": "normal",
  "init_range": 0.01,
  "init_std": 0.02,
  "mem_len": 1600,
  "n_head": 16,
  "n_layer": 18,
  "n_token": 267735,
  "num_labels": 2,
  "output_attentions": false,
  "output_hidden_states": false,
  "pre_lnorm": false,
  "proj_init_std": 0.01,
  "same_length": true,
  "sample_softmax": -1,
  "tgt_len": 128,
  "tie_projs": [
    false,
    true,
    true,
    true
  ],
  "tie_weight": true,
  "torchscript": false,
  "untie_r": true
}

07/16/2019 18:01:53 - INFO - pytorch_transformers.modeling_utils -   loading weights file https://s3.amazonaws.com/models.huggingface.co/bert/transfo-xl-wt103-pytorch_model.bin from cache at /home/korymathewson/.cache/torch/pytorch_transformers/12642ff7d0279757d8356bfd86a729d9697018a0c93ad042de1d0d2cc17fd57b.e9704971f27275ec067a00a67e6a5f0b05b4306b3f714a96e9f763d8fb612671
07/16/2019 18:02:06 - INFO - __main__ -   Evaluating with bsz 10 tgt_len 128 ext_len 0 mem_len 1600 clamp_len 1000
Traceback (most recent call last):
  File "run_transfo_xl.py", line 153, in <module>
    main()
  File "run_transfo_xl.py", line 134, in main
    test_loss = evaluate(te_iter)
  File "run_transfo_xl.py", line 117, in evaluate
    loss, mems = ret
ValueError: too many values to unpack (expected 2)
```

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