improve final answer extraction in utils_squad.py
Shouldn't ` get_final_text` use the specific optionally pre-trained tokenizer instead of generically using `BasicTokenizer` ?

[examples/utils_squad.py L911](https://github.com/huggingface/transformers/blob/6596e3d56626c921b3920e313866b7412633b91a/examples/utils_squad.py#L911)
Any update?<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
