Update README.md
Update AutoModel & AutoTokenizer loading.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3603?src=pr&el=h1) Report
> Merging [#3603](https://codecov.io/gh/huggingface/transformers/pull/3603?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/81484b447b7d8504ff5e1cfff38ec35918383963&el=desc) will **not change** coverage by `%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/3603/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/3603?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #3603   +/-   ##
=======================================
  Coverage   78.06%   78.06%           
=======================================
  Files         100      100           
  Lines       17134    17134           
=======================================
  Hits        13375    13375           
  Misses       3759     3759           
```



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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3603?src=pr&el=footer). Last update [81484b4...32340ca](https://codecov.io/gh/huggingface/transformers/pull/3603?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
