How to use with ElasticSearch?

I have been trying to use it with ElasticSearch this way:

```py
mapping = schema_to_mapping(json_schema, root_url, {}, ElasticMappingGeneratorConfig())
mappings = {indexname: mapping}
client = elasticsearch.Elasticsearch(hosts)
client.indices.create(index=indexname,
body={"mappings": mappings})
```
...but got the following error:

```
{"error":{"root_cause":[{"type":"mapper_parsing_exception","reason":"Mapping definition for [_all] has unsupported parameters: [enable : true]"}],"type":"mapper_parsing_exception","reason":"Failed to parse mapping [kinto-bid-cid]: Mapping definition for [_all] has unsupported parameters: [enable : true]","caused_by":{"type":"mapper_parsing_exception","reason":"Mapping definition for [_all] has unsupported parameters: [enable : true]"}},"status":400}
```

I could get it to work by stripping out some part of the result of `schema_to_mapping`:

```python
mapping = schema_to_mapping(json_schema, root_url, {}, ElasticMappingGeneratorConfig())
mapping = {"properties": mapping["properties"]}
```

Am I doing something wrong? Is this expected?

Thanks for the tool :)