The problem: ElasticSearch.pm is a module that has existed for some time on the CPAN. Elasticsearch.pm has just been uploaded quite recently, presenting a new API, but its installation will overwrite any existing ElasticSearch.pm on case-insensitive file systems.
https://metacpan.org/module/ElasticSearch#DEPRECATION comments requested, on how to resolve this issue: https://github.com/elasticsearch/elasticsearch-perl/issues/5
