Update reverse proxy config for _mapping

Hi there.  I'm having trouble with the latest chef-logstash plus the latest chef-kibana cookbooks.  Kibana is trying the following request which is failing:

http://logstash-server:/logstash-2014.02.18,logstash-2014.02.17/_mapping/field/*

I'm not sure whether this is something new with Kibana or what so I'm proposing this fix to get some comments.  Obviously the apache2 proxy configuration will need to be updated as well.