Issue: Cannot download ade_corpus_v2

I tried this to get the dataset following this url : https://huggingface.co/datasets/ade_corpus_v2

but received this error : 

`Traceback (most recent call last):
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/load.py", line 267, in prepare_module
    local_path = cached_path(file_path, download_config=download_config)
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/utils/file_utils.py", line 308, in cached_path
    use_etag=download_config.use_etag,
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/utils/file_utils.py", line 486, in get_from_cache
    raise FileNotFoundError("Couldn't find file at {}".format(url))
FileNotFoundError: Couldn't find file at https://raw.githubusercontent.com/huggingface/datasets/1.1.3/datasets/ade_corpus_v2/ade_corpus_v2.py

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/load.py", line 278, in prepare_module
    local_path = cached_path(file_path, download_config=download_config)
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/utils/file_utils.py", line 308, in cached_path
    use_etag=download_config.use_etag,
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/utils/file_utils.py", line 486, in get_from_cache
    raise FileNotFoundError("Couldn't find file at {}".format(url))
FileNotFoundError: Couldn't find file at https://s3.amazonaws.com/datasets.huggingface.co/datasets/datasets/ade_corpus_v2/ade_corpus_v2.py

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/load.py", line 589, in load_dataset
    path, script_version=script_version, download_config=download_config, download_mode=download_mode, dataset=True
  File "/opt/anaconda3/lib/python3.7/site-packages/datasets/load.py", line 282, in prepare_module
    combined_path, github_file_path, file_path
FileNotFoundError: Couldn't find file locally at ade_corpus_v2/ade_corpus_v2.py, or remotely at https://raw.githubusercontent.com/huggingface/datasets/1.1.3/datasets/ade_corpus_v2/ade_corpus_v2.py or https://s3.amazonaws.com/datasets.huggingface.co/datasets/datasets/ade_corpus_v2/ade_corpus_v2.py`




Comments:
Hi @him1411, the dataset you are trying to load has been added during the community sprint and has not been released yet. It will be available with the v2 of `datasets`.
For now, you should be able to load the datasets after installing the latest (master) version of `datasets` using pip:
`pip install git+https://github.com/huggingface/datasets.git@master`

`ade_corpus_v2` was added recently, that's why it wasn't available yet.

To load it you can just update `datasets`
```
pip install --upgrade datasets
```

and then you can load `ade_corpus_v2` with

```python
from datasets import load_dataset

dataset = load_dataset("ade_corpus_v2", "Ade_corpos_v2_drug_ade_relation")
```

(looks like there is a typo in the configuration name, we'll fix it for the v2.0 release of `datasets` soon)