Missing required argument 'mode' in run_ner.
## 🐛 Bug

<!-- Important information -->

Model I am using: BERT

Language I am using the model on: Polish (irrelevant for the error)

The problem arise when using:
* [x] the official example scripts: run_ner.py

The tasks I am working on is:
* [x] my own task or dataset: token classification (aka NER)

## To Reproduce

Steps to reproduce the behavior:

1. Start run_ner.py with --evaluate_during_training
2. During evaluation the error will happen


## Expected behavior

Evaluation should run fine

## Additional context

There is a missing argument in line 156 `mode`, which (I belive) should be `"dev"`.
I can provide a PR if the above solution is confirmed.
yes sure, happy to welcome a PR on this<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
