Update metric table in README.md
Update metric table in README.md

jdgwartney/meter-plugin-rabbitmq,jdgwartney/boundary-plugin-rabbitmq,jdgwartney/meter-plugin-rabbitmq,boundary/boundary-plugin-rabbitmq,boundary/boundary-plugin-rabbitmq,boundary/plugin-rabbitmq,boundary/plugin-rabbitmq,jdgwartney/meter-plugin-rabbitmq,jdgwartney/boundary-plugin-rabbitmq,boundary/boundary-plugin-rabbitmq,jdgwartney/boundary-plugin-rabbitmq,boundary/plugin-rabbitmq,boundary/meter-plugin-rabbitmq,boundary/meter-plugin-rabbitmq,boundary/meter-plugin-rabbitmq