ElasticSearch Indexing example: TypeError: __init__() missing 1 required positional argument: 'scheme'
## Describe the bug
I am following the example in the documentation for elastic search step by step (on google colab): https://huggingface.co/docs/datasets/faiss_es#elasticsearch

```
from datasets import load_dataset
squad = load_dataset('crime_and_punish', split='train[:1000]')
```

When I run the line: 
`squad.add_elasticsearch_index("context", host="localhost", port="9200")`

I get the error: 
`TypeError: __init__() missing 1 required positional argument: 'scheme'`


## Expected results
No error message

## Actual results

```
TypeError                                 Traceback (most recent call last)

[<ipython-input-23-9205593edef3>](https://localhost:8080/#) in <module>()
      1 import elasticsearch
----> 2 squad.add_elasticsearch_index("text", host="localhost", port="9200")


6 frames

[/usr/local/lib/python3.7/dist-packages/elasticsearch/_sync/client/utils.py](https://localhost:8080/#) in host_mapping_to_node_config(host)
    209         options["path_prefix"] = options.pop("url_prefix")
    210 
--> 211     return NodeConfig(**options)  # type: ignore
    212 
    213 

TypeError: __init__() missing 1 required positional argument: 'scheme'
```

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 2.2.0
- Platform: Linux, Google Colab
- Python version: Google Colab (probably 3.7)
- PyArrow version: ?
