Add missing arg in 02-transformers notebook
Author: pri-ax
Pull request: yes

Add missing `from_tf=True` arg when creating the model `AutoModel.from_pretrained()` to avoid an OSError from loading a PyTorch model from a TF 2.0 checkpoint.

Also fixed two small typos in markdown text.

Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5085?src=pr&el=h1) Report
> Merging [#5085](https://codecov.io/gh/huggingface/transformers/pull/5085?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/7291ea0bff57a017e71b1ea8ec01ff19da298bf0&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/5085/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/5085?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #5085      +/-   ##
==========================================
- Coverage   77.24%   77.22%   -0.02%     
==========================================
  Files         133      133              
  Lines       22146    22146              
==========================================
- Hits        17107    17103       -4     
- Misses       5039     5043       +4     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/5085?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5085/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `85.86% <0.00%> (-0.78%)` | :arrow_down: |
| [src/transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5085/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ191dGlscy5weQ==) | `90.61% <0.00%> (-0.12%)` | :arrow_down: |
| [src/transformers/modeling\_transfo\_xl.py](https://codecov.io/gh/huggingface/transformers/pull/5085/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190cmFuc2ZvX3hsLnB5) | `78.81% <0.00%> (+0.19%)` | :arrow_up: |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5085/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `75.40% <0.00%> (+0.40%)` | :arrow_up: |

------

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Hi, I agree with the typo change, but there's no need for the `from_tf` flag. `bert-base-cased` is available in both TensorFlow and PyTorch, so there's no need for the flag.

@LysandreJik you're right! I was getting an error unless I explicitly passed `from_tf=True` yesterday, but not today. Since I can't reproduce it, I'll remove that change.