overflow_to_sample_mapping missing in in documentation
In the [documentation ]( https://huggingface.co/transformers/master/main_classes/tokenizer.html#transformers.PreTrainedTokenizerFast.__call__)of the fast tokenizer, the `overflow_to_sample_mapping` field is missing.
Instead the `overflowing_tokens`  is listed there, which is only part of  the base tokenizer.

Indeed! Do you want to open a PR with a fix?<|||||>No not really. 
But I've found that the documentation is the same because the `PreTrainedTokenizerFast` inherits the `__call__` method as well as the documentation from `PreTrainedTokenizerBase`. 
The `__call__` method documentation is a concatenation of two different documentations.
So changing that single line of documentation is more complicated than I expected.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>I think that it does?