Release 0.19.4.
Release 0.19.4.

* ENG-2750: Add cluster name to json logging.

* ENG-2658: Fix condition where request accessed from separate response thread.

tmayfield/elasticsearch-jetty,paul-e-cooley/elasticsearch-jetty,paul-e-cooley/elasticsearch-jetty,whitefoxx/elasticsearch-jetty,JoeyJiao/elasticsearch-jetty,sonian/elasticsearch-jetty,whitefoxx/elasticsearch-jetty,JoeyJiao/elasticsearch-jetty,sonian/elasticsearch-jetty,tmayfield/elasticsearch-jetty