fixing xlm-roberta tokenizer max_length and automodels
Author: thomwolf
Pull request: yes

Fix missing max token num in XLM-Roberta

Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2243?src=pr&el=h1) Report
> Merging [#2243](https://codecov.io/gh/huggingface/transformers/pull/2243?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/65c75fc58796b278d58b0ce2c8d2031594ef0f64?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `21.42%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2243/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2243?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #2243      +/-   ##
==========================================
- Coverage    79.9%   79.88%   -0.03%     
==========================================
  Files         131      131              
  Lines       19451    19467      +16     
==========================================
+ Hits        15543    15551       +8     
- Misses       3908     3916       +8
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2243?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2243/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3V0aWxzLnB5) | `94.1% <ø> (+1.07%)` | :arrow_up: |
| [transformers/commands/run.py](https://codecov.io/gh/huggingface/transformers/pull/2243/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL2NvbW1hbmRzL3J1bi5weQ==) | `0% <0%> (ø)` | :arrow_up: |
| [transformers/tokenization\_xlm\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/2243/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl94bG1fcm9iZXJ0YS5weQ==) | `36.92% <0%> (ø)` | :arrow_up: |
| [transformers/tokenization\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2243/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl91dGlscy5weQ==) | `92.08% <100%> (+0.01%)` | :arrow_up: |
| [transformers/modeling\_auto.py](https://codecov.io/gh/huggingface/transformers/pull/2243/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX2F1dG8ucHk=) | `31.92% <18.18%> (-1.09%)` | :arrow_down: |
| [transformers/pipelines.py](https://codecov.io/gh/huggingface/transformers/pull/2243/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3BpcGVsaW5lcy5weQ==) | `67.65% <27.58%> (+0.49%)` | :arrow_up: |
| [transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2243/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX3V0aWxzLnB5) | `93.15% <0%> (-0.53%)` | :arrow_down: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2243?src=pr&el=footer). Last update [65c75fc...bbaaec0](https://codecov.io/gh/huggingface/transformers/pull/2243?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).