fields parameter has been replaced by stored_fields

[haarg]

https://www.elastic.co/guide/en/elasticsearch/reference/5.0/breaking_50_search_changes.html#_literal_fields_literal_parameter

[haarg]

In most cases, we should just be getting data from _source rather than fields.

For anything that we do need to use fields, this will be a problem to do with ElasticSearchX::Model. Most of the queries using ESXModel can be rewritten to use Search::Elasticsearch instead.