Issue: conll 2003 dataset source url is no longer valid

Comment:
Hello! Unfortunately, this URL does not work for me. 
Could you please tell me how I can solve the problem?

`>>> from datasets import load_dataset
>>> dataset = load_dataset("conll2003")
Downloading and preparing dataset conll2003/conll2003 (download: 4.63 MiB, generated: 9.78 MiB, post-processed: Unknown size, total: 14.41 MiB) to /home/dafedo/.cache/huggingface/datasets/conll2003/conll2003/1.0.0/40e7cb6bcc374f7c349c83acd1e9352a4f09474eb691f64f364ee62eb65d0ca6...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/load.py", line 745, in load_dataset
    builder_instance.download_and_prepare(
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/builder.py", line 574, in download_and_prepare
    self._download_and_prepare(
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/builder.py", line 630, in _download_and_prepare
    split_generators = self._split_generators(dl_manager, **split_generators_kwargs)
  File "/home/dafedo/.cache/huggingface/modules/datasets_modules/datasets/conll2003/40e7cb6bcc374f7c349c83acd1e9352a4f09474eb691f64f364ee62eb65d0ca6/conll2003.py", line 196, in _split_generators
    downloaded_files = dl_manager.download_and_extract(urls_to_download)
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/download_manager.py", line 287, in download_and_extract
    return self.extract(self.download(url_or_urls))
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/download_manager.py", line 195, in download
    downloaded_path_or_paths = map_nested(
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/py_utils.py", line 203, in map_nested
    mapped = [
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/py_utils.py", line 204, in <listcomp>
    _single_map_nested((function, obj, types, None, True)) for obj in tqdm(iterable, disable=disable_tqdm)
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/py_utils.py", line 142, in _single_map_nested
    return function(data_struct)
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/download_manager.py", line 218, in _download
    return cached_path(url_or_filename, download_config=download_config)
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/file_utils.py", line 281, in cached_path
    output_path = get_from_cache(
  File "/home/dafedo/efficient-task-transfer/venv/lib/python3.8/site-packages/datasets/utils/file_utils.py", line 621, in get_from_cache
    raise FileNotFoundError("Couldn't find file at {}".format(url))
FileNotFoundError: Couldn't find file at https://github.com/davidsbatista/NER-datasets/raw/master/CONLL2003/train.txt
`

I receive the same error when I run "itrain run_configs/conll2003.json" from https://github.com/adapter-hub/efficient-task-transfer

Thank you very much in advance!

Regards, 
Daria