Updates args in tf squad example. (#4820)

Co-authored-by: Daniel Shan <daniel.shan@workday.com>

examples/question-answering/README.md

@@ -165,17 +165,15 @@ Larger batch size may improve the performance while costing more memory.
 python run_tf_squad.py \
     --model_name_or_path bert-base-uncased \
     --output_dir model \
-    --max-seq-length 384 \
+    --max_seq_length 384 \
     --num_train_epochs 2 \
     --per_gpu_train_batch_size 8 \
     --per_gpu_eval_batch_size 16 \
     --do_train \
     --logging_dir logs \    
-    --mode question-answering \
     --logging_steps 10 \
     --learning_rate 3e-5 \
-    --doc_stride 128 \
-    --optimizer_name adamw
+    --doc_stride 128    
 ```
 
 For the moment the evaluation is not available in the Tensorflow Trainer only the training.