load_dataset for CSV files not working
Hi, 
I got an `OSError: Cannot find data file. ` when I tried to use load_dataset with tsv files. I have checked the paths, and they are correct.  

versions
- python: 3.7.9
- datasets: 1.1.3
- pyarrow: 2.0.0
- transformers: 4.2.2

~~~
data_files = {"train": "train.tsv", "test",: "test.tsv"}
datasets = load_dataset("csv", data_files=data_files, delimiter="\t")
~~~

The entire Error message is on below:

```08/14/2021 16:55:44 - INFO - __main__ -   load a local file for train: /project/media-framing/transformer4/data/0/val/label1.tsv
08/14/2021 16:55:44 - INFO - __main__ -   load a local file for test: /project/media-framing/transformer4/data/unlabel/test.tsv
Using custom data configuration default
Downloading and preparing dataset csv/default-00a4200ae8507533 (download: Unknown size, generated: Unknown size, post-processed: Unknown size, total: Unknown size) to /usr4/cs542sp/hey1/.cache/huggingface/datasets/csv/default-00a4200ae8507533/0.0.0/2960f95a26e85d40ca41a230ac88787f715ee3003edaacb8b1f0891e9f04dda2...
Traceback (most recent call last):
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 592, in _download_and_prepare
    self._prepare_split(split_generator, **prepare_split_kwargs)
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 944, in _prepare_split
    num_examples, num_bytes = writer.finalize()
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/arrow_writer.py", line 307, in finalize
    self.stream.close()
  File "pyarrow/io.pxi", line 132, in pyarrow.lib.NativeFile.close
  File "pyarrow/error.pxi", line 99, in pyarrow.lib.check_status
OSError: error closing file

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "run_glue.py", line 484, in <module>
    main()
  File "run_glue.py", line 243, in main
    datasets = load_dataset("csv", data_files=data_files, delimiter="\t")
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/load.py", line 610, in load_dataset
    ignore_verifications=ignore_verifications,
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 515, in download_and_prepare
    dl_manager=dl_manager, verify_infos=verify_infos, **download_and_prepare_kwargs
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 594, in _download_and_prepare
    raise OSError("Cannot find data file. " + (self.manual_download_instructions or ""))
OSError: Cannot find data file. ```
Similar to #622, I've noticed there is a problem when trying to load a CSV file with datasets.

`
from datasets import load_dataset
`
`
dataset = load_dataset("csv", data_files=["./sample_data.csv"], delimiter="\t", column_names=["title", "text"], script_version="master")
`

Displayed error:
`
...
ArrowInvalid: CSV parse error: Expected 2 columns, got 1
`

I should mention that when I've tried to read data from `https://github.com/lhoestq/transformers/tree/custom-dataset-in-rag-retriever/examples/rag/test_data/my_knowledge_dataset.csv` it worked without a problem. I've read that there might be some problems with /r character, so I've removed them from the custom dataset, but the problem still remains.

I've added a colab reproducing the bug, but unfortunately I cannot provide the dataset.
https://colab.research.google.com/drive/1Qzu7sC-frZVeniiWOwzoCe_UHZsrlxu8?usp=sharing

Are there any work around for it ?
Thank you
load_dataset for CSV files not working 
 Similar to #622, I've noticed there is a problem when trying to load a CSV file with datasets.

`
from datasets import load_dataset
`
`
dataset = load_dataset("csv", data_files=["./sample_data.csv"], delimiter="\t", column_names=["title", "text"], script_version="master")
`

Displayed error:
`
...
ArrowInvalid: CSV parse error: Expected 2 columns, got 1
`

I should mention that when I've tried to read data from `https://github.com/lhoestq/transformers/tree/custom-dataset-in-rag-retriever/examples/rag/test_data/my_knowledge_dataset.csv` it worked without a problem. I've read that there might be some problems with /r character, so I've removed them from the custom dataset, but the problem still remains.

I've added a colab reproducing the bug, but unfortunately I cannot provide the dataset.
https://colab.research.google.com/drive/1Qzu7sC-frZVeniiWOwzoCe_UHZsrlxu8?usp=sharing

Are there any work around for it ?
Thank you 
 Hi, 
I got an `OSError: Cannot find data file. ` when I tried to use load_dataset with tsv files. I have checked the paths, and they are correct.  

versions
- python: 3.7.9
- datasets: 1.1.3
- pyarrow: 2.0.0
- transformers: 4.2.2

~~~
data_files = {"train": "train.tsv", "test",: "test.tsv"}
datasets = load_dataset("csv", data_files=data_files, delimiter="\t")
~~~

The entire Error message is on below:

```08/14/2021 16:55:44 - INFO - __main__ -   load a local file for train: /project/media-framing/transformer4/data/0/val/label1.tsv
08/14/2021 16:55:44 - INFO - __main__ -   load a local file for test: /project/media-framing/transformer4/data/unlabel/test.tsv
Using custom data configuration default
Downloading and preparing dataset csv/default-00a4200ae8507533 (download: Unknown size, generated: Unknown size, post-processed: Unknown size, total: Unknown size) to /usr4/cs542sp/hey1/.cache/huggingface/datasets/csv/default-00a4200ae8507533/0.0.0/2960f95a26e85d40ca41a230ac88787f715ee3003edaacb8b1f0891e9f04dda2...
Traceback (most recent call last):
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 592, in _download_and_prepare
    self._prepare_split(split_generator, **prepare_split_kwargs)
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 944, in _prepare_split
    num_examples, num_bytes = writer.finalize()
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/arrow_writer.py", line 307, in finalize
    self.stream.close()
  File "pyarrow/io.pxi", line 132, in pyarrow.lib.NativeFile.close
  File "pyarrow/error.pxi", line 99, in pyarrow.lib.check_status
OSError: error closing file

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "run_glue.py", line 484, in <module>
    main()
  File "run_glue.py", line 243, in main
    datasets = load_dataset("csv", data_files=data_files, delimiter="\t")
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/load.py", line 610, in load_dataset
    ignore_verifications=ignore_verifications,
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 515, in download_and_prepare
    dl_manager=dl_manager, verify_infos=verify_infos, **download_and_prepare_kwargs
  File "/projectnb2/media-framing/env-trans4/lib/python3.7/site-packages/datasets/builder.py", line 594, in _download_and_prepare
    raise OSError("Cannot find data file. " + (self.manual_download_instructions or ""))
OSError: Cannot find data file. ```