Fix the example command for SQuAD
Issue #4549: added the missing argument `--do_lower_case` for reproducing the intended results.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4561?src=pr&el=h1) Report
> Merging [#4561](https://codecov.io/gh/huggingface/transformers/pull/4561?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/a34a9896ac2a4a33ff9cd805c76eed914c8d8965&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4561/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4561?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #4561      +/-   ##
==========================================
- Coverage   77.87%   77.86%   -0.02%     
==========================================
  Files         123      123              
  Lines       20566    20566              
==========================================
- Hits        16016    16013       -3     
- Misses       4550     4553       +3     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4561?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4561/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `73.44% <0.00%> (-0.42%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4561/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `88.50% <0.00%> (-0.17%)` | :arrow_down: |
| [src/transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4561/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ191dGlscy5weQ==) | `90.41% <0.00%> (-0.12%)` | :arrow_down: |

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<|||||>Can you add the do_lower_case flag for all other instances in that README that use bert uncased? Thanks!<|||||>Sure. Presumably for the tf version, the script will handle the casings automatically.<|||||>From the code it would seem that way, but I am not sure actually. 

cc @thomwolf @LysandreJik: `do_lower_case` was missing in the commands to run squad with bert-base-uncased. Is this flag also necessary in the Tensorflow version? It's not present in the code, so I would assume not.

The other changes LGTM!<|||||>Closed by #4245 (we still need to investigate why the lowercasing is not properly populated by the model's config)