Digging deeper into the rabbit hole I discovered I needed to specify the path to jruby to run the gem install command. When running the following command I now see missing dependency for manticore v0.5.2.
env GEM_HOME=/opt/logstash/vendor/bundle/jruby/1.9 /opt/logstash/vendor/jruby/bin/jruby /opt/logstash/vendor/jruby/bin/gem install manticore -v '0.5.2'
it was missing an xml file that was supposed to be included with ruby-maven 3.3.8.
The following 2 commands got me back up and running with logstash-output-elasticsearch v2.3.1:
[user@host ~]# env GEM_HOME=/opt/logstash/vendor/bundle/jruby/1.9 /opt/logstash/vendor/jruby/bin/jruby /opt/logstash/vendor/jruby/bin/gem install ruby-maven
this installed the lastest v.3.3.8 of ruby-maven and then I ran
[user@host ~]# env GEM_HOME=/opt/logstash/vendor/bundle/jruby/1.9 /opt/logstash/vendor/jruby/bin/jruby /opt/logstash/vendor/jruby/bin/gem install manticore -v '0.5.2'
after that install completed successfully I was able to restart logstash. Hope this helps!