Error in NER examples, run.sh
Author: pradeepkr12
Pull request: no

## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `transformers` version: 3.5.1
- Platform: Linux-4.19.112+-x86_64-with-Ubuntu-18.04-bionic
- Python version: 3.6.9
- PyTorch version (GPU?): 1.7.0+cu101 (True)
- Tensorflow version (GPU?): 2.3.0 (True)
- Using GPU in script?: Yes
- Using distributed or parallel set-up in script?: No

### Who can help
<!-- Your issue will be replied to more quickly if you can figure out the right person to tag with @
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 Please tag fewer than 3 people.
 @stefan-it
 albert, bert, GPT2, XLM: @LysandreJik 
 tokenizers: @mfuntowicz
 Trainer: @sgugger
 Speed and Memory Benchmarks: @patrickvonplaten
 Model Cards: @julien-c
 TextGeneration: @TevenLeScao 
 examples/distillation: @VictorSanh
 nlp datasets: [different repo](https://github.com/huggingface/nlp)
 rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)
 Text Generation: @patrickvonplaten @TevenLeScao
 Blenderbot: @patrickvonplaten
 Bart: @patrickvonplaten
 Marian: @patrickvonplaten
 Pegasus: @patrickvonplaten
 mBART: @patrickvonplaten
 T5: @patrickvonplaten
 Longformer/Reformer: @patrickvonplaten
 TransfoXL/XLNet: @TevenLeScao
 RAG: @patrickvonplaten, @lhoestq
 FSMT: @stas00
 examples/seq2seq: @patil-suraj
 examples/bert-loses-patience: @JetRunner
 tensorflow: @jplu
 examples/token-classification: @stefan-it
 documentation: @sgugger
 -->
## Information

Model I am using (Bert, XLNet ...):
Bert
The problem arises when using:
* [x] the official example scripts: (give details below)
examples/token-classification/run.sh
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
NER with conll2003 dataset
* [ ] an official GLUE/SQUaD task: (give the name)
* [ ] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:

1. !sh examples/token-classification/run.sh
2.
3.

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Error traceback

Traceback (most recent call last):
  File "run_ner.py", line 383, in <module>
    main()
  File "run_ner.py", line 285, in main
    load_from_cache_file=not data_args.overwrite_cache,
  File "/usr/local/lib/python3.6/dist-packages/datasets/dataset_dict.py", line 300, in map
    for k, dataset in self.items()
  File "/usr/local/lib/python3.6/dist-packages/datasets/dataset_dict.py", line 300, in <dictcomp>
    for k, dataset in self.items()
  File "/usr/local/lib/python3.6/dist-packages/datasets/arrow_dataset.py", line 1256, in map
    update_data=update_data,
  File "/usr/local/lib/python3.6/dist-packages/datasets/arrow_dataset.py", line 156, in wrapper
    out: Union["Dataset", "DatasetDict"] = func(self, *args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/datasets/fingerprint.py", line 158, in wrapper
    self._fingerprint, transform, kwargs_for_fingerprint
  File "/usr/local/lib/python3.6/dist-packages/datasets/fingerprint.py", line 105, in update_fingerprint
    hasher.update(transform_args[key])
  File "/usr/local/lib/python3.6/dist-packages/datasets/fingerprint.py", line 57, in update
    self.m.update(self.hash(value).encode("utf-8"))
  File "/usr/local/lib/python3.6/dist-packages/datasets/fingerprint.py", line 53, in hash
    return cls.hash_default(value)
  File "/usr/local/lib/python3.6/dist-packages/datasets/fingerprint.py", line 46, in hash_default
    return cls.hash_bytes(dumps(value))
  File "/usr/local/lib/python3.6/dist-packages/datasets/utils/py_utils.py", line 367, in dumps
    dump(obj, file)
  File "/usr/local/lib/python3.6/dist-packages/datasets/utils/py_utils.py", line 339, in dump
    Pickler(file, recurse=True).dump(obj)
  File "/usr/local/lib/python3.6/dist-packages/dill/_dill.py", line 454, in dump
    StockPickler.dump(self, obj)
  File "/usr/lib/python3.6/pickle.py", line 409, in dump
    self.save(obj)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/lib/python3.6/dist-packages/dill/_dill.py", line 1447, in save_function
    obj.__dict__, fkwdefaults), obj=obj)
  File "/usr/lib/python3.6/pickle.py", line 610, in save_reduce
    save(args)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python3.6/pickle.py", line 751, in save_tuple
    save(element)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python3.6/pickle.py", line 751, in save_tuple
    save(element)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/lib/python3.6/dist-packages/dill/_dill.py", line 1178, in save_cell
    pickler.save_reduce(_create_cell, (f,), obj=obj)
  File "/usr/lib/python3.6/pickle.py", line 610, in save_reduce
    save(args)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python3.6/pickle.py", line 736, in save_tuple
    save(element)
  File "/usr/lib/python3.6/pickle.py", line 521, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/lib/python3.6/pickle.py", line 605, in save_reduce
    save(cls)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/lib/python3.6/dist-packages/dill/_dill.py", line 1374, in save_type
    obj.__bases__, _dict), obj=obj)
  File "/usr/lib/python3.6/pickle.py", line 610, in save_reduce
    save(args)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python3.6/pickle.py", line 751, in save_tuple
    save(element)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/lib/python3.6/dist-packages/dill/_dill.py", line 941, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/usr/lib/python3.6/pickle.py", line 821, in save_dict
    self._batch_setitems(obj.items())
  File "/usr/lib/python3.6/pickle.py", line 847, in _batch_setitems
    save(v)
  File "/usr/lib/python3.6/pickle.py", line 476, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/lib/python3.6/dist-packages/dill/_dill.py", line 941, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/usr/lib/python3.6/pickle.py", line 821, in save_dict
    self._batch_setitems(obj.items())
  File "/usr/lib/python3.6/pickle.py", line 847, in _batch_setitems
    save(v)
  File "/usr/lib/python3.6/pickle.py", line 507, in save
    self.save_global(obj, rv)
  File "/usr/lib/python3.6/pickle.py", line 927, in save_global
    (obj, module_name, name))
_pickle.PicklingError: Can't pickle typing.Union[str, NoneType]: it's not the same object as typing.Union
## Expected behavior
It should train and evaluate, give accuracy details.
<!-- A clear and concise description of what you would expect to happen. -->


Comments:
Can confirm that this also appears on latest master (0a80959bddd5da08742d22dca07e0facf0b4cd11)

Related to: #8212

Yes. 
Thanks, I managed to install py 3.8 in Colab and ran it successfully.