Unexpected behavior when loading cached csv file?
Hi ! Thanks for reporting.
The same issue was reported in #730 (but with the encodings instead of the delimiter). It was fixed by #770 .
The fix will be available in the next release :) Thanks for the prompt reply and terribly sorry for the spam! 
Looking forward to the new release! 
I read a csv file from disk and forgot so specify the right delimiter. When i read the csv file again specifying the right delimiter it had no effect since it was using the cached dataset. I am not sure if this is unwanted behavior since i can always specify `download_mode="force_redownload"`. But i think it would be nice if the information what `delimiter` or what `column_names` were used would influence the identifier of the cached dataset.

Small snippet to reproduce the behavior:
```python
import datasets

with open("dummy_data.csv", "w") as file:
    file.write("test,this;text\n")

print(datasets.load_dataset("csv", data_files="dummy_data.csv", split="train").column_names)
# ["test", "this;text"]

print(datasets.load_dataset("csv", data_files="dummy_data.csv", split="train", delimiter=";").column_names)
# still ["test", "this;text"]
```

By the way, thanks a lot for this amazing library! :)