Pretrain experiment missing `restrict_attention_bucket_size` command line flag definition

[maxploter]

An AttributeError for the restrict_attention_bucket_size flag is raised when running the tapas_pretraining_experiment script. Explicitly providing the command line flag doesn't solve the the problem (Unknown command line flag 'restrict_attention_bucket_size').
Probably, the flag was not defined in the script file during changes related to MATE?

@eisenjulian I wonder if the command line flag was overlooked in the following commit?
733aca5

Command:

python tapas/experiments/tapas_pretraining_experiment.py \
  --eval_batch_size=32 \
  --train_batch_size=512 \
  --num_eval_steps=100 \
  --save_checkpoints_steps=5000 \
  --num_train_examples=512000000 \
  --max_seq_length=128 \
  --input_file_train="uncased_L-2_H-128_A-2/results_sample/train.tfrecord" \
  --input_file_eval="uncased_L-2_H-128_A-2/results_sample/test.tfrecord" \
  --init_checkpoint="uncased_L-2_H-128_A-2/bert_model.ckpt.data-00000-of-00001" \
  --bert_config_file="uncased_L-2_H-128_A-2/bert_config.json" \
  --model_dir="uncased_L-2_H-128_A-2" \
  --do_train

Stacktrace:

Traceback (most recent call last):
  File "tapas/experiments/tapas_pretraining_experiment.py", line 193, in <module>
    app.run(main)
  File "/gpfs/space/home/ploter/.conda/envs/tapas_clean_env/lib/python3.7/site-packages/absl/app.py", line 308, in run
    _run_main(main, args)
  File "/gpfs/space/home/ploter/.conda/envs/tapas_clean_env/lib/python3.7/site-packages/absl/app.py", line 254, in _run_main
    sys.exit(main(argv))
  File "tapas/experiments/tapas_pretraining_experiment.py", line 125, in main
    restrict_attention_bucket_size=FLAGS.restrict_attention_bucket_size,
  File "/gpfs/space/home/ploter/.conda/envs/tapas_clean_env/lib/python3.7/site-packages/absl/flags/_flagvalues.py", line 474, in __getattr__
    raise AttributeError(name)
AttributeError: restrict_attention_bucket_size