.map() function got an unexpected keyword argument 'cache_file_name'
Hi @cindyxinyiwang,
Did you try adding `.arrow` after `cache_file_name` argument? Here I think they're expecting something like that only for a cache file:
https://github.com/huggingface/datasets/blob/e08362256fb157c0b3038437fc0d7a0bbb50de5c/src/datasets/arrow_dataset.py#L1556-L1558 Hi ! `cache_file_name` is an argument of the `Dataset.map` method. Can you check that your `dataset` is indeed a `Dataset` object ?

If you loaded several splits, then it would actually be a `DatasetDict` (one dataset per split, in a dictionary).
In this case, since there are several datasets in the dict, the `DatasetDict.map` method requires a `cache_file_names` argument (with an 's'), so that you can provide one file name per split. I think you are right. I used cache_file_names={data1: name1, data2: name2} and it works. Thank you!
## Describe the bug

I'm trying to save the result of datasets.map() to a specific file, so that I can easily share it among multiple computers without reprocessing the dataset. However, when I try to pass an argument 'cache_file_name' to the .map() function, it throws an error that ".map() function got an unexpected keyword argument 'cache_file_name'". 

I believe I'm using the latest dataset 1.6.2. Also seems like the document and the actual code indicates there is an argument 'cache_file_name' for the .map() function.

Here is the code I use
## Steps to reproduce the bug
```datasets = load_from_disk(dataset_path=my_path)

[...]

def tokenize_function(examples):
    return tokenizer(examples[text_column_name])

logger.info("Mapping dataset to tokenized dataset.")
tokenized_datasets = datasets.map(
    tokenize_function,
    batched=True,
    num_proc=preprocessing_num_workers,
    remove_columns=column_names,
    load_from_cache_file=True,
   cache_file_name="my_tokenized_file"
)
```

## Actual results
    tokenized_datasets = datasets.map(
TypeError: map() got an unexpected keyword argument 'cache_file_name'

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version:1.6.2
- Platform:Linux-4.18.0-193.28.1.el8_2.x86_64-x86_64-with-glibc2.10
- Python version:3.8.5
- PyArrow version:3.0.0
