Add `tokenizer_max_length` to `cardiffnlp/twitter-roberta-base-sentiment`
[cardiffnlp/twitter-roberta-base-sentiment](https://huggingface.co/cardiffnlp/twitter-roberta-base-sentiment) is one of the most downloaded `text-classification` models on the hub. 
But there is a small little bug, when using the model with `seq_len` > 515, see image
![image](https://user-images.githubusercontent.com/32632186/132306231-60ba797c-baf6-434d-bcf7-0229f2e1cd80.png)

To fix this we would need to add `tokenizer_max_length` attribute in a `tokenizer_config.json` on the hub for that model. 
@cardiffnlp would it be okay for you to add it? I am happy to make the change. 
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