Fixes dockerfile from pointing to the dead Bintray to the current RabbitMQ image

Author: aurban-iqmessenger

docker/Dockerfile

@@ -1,16 +1,4 @@
-FROM ubuntu:18.04
-
-RUN apt-get update -y
-RUN apt-get install -y gnupg2 wget
-RUN wget -O - "https://github.com/rabbitmq/signing-keys/releases/download/2.0/rabbitmq-release-signing-key.asc" | apt-key add -
-
-COPY apt/sources.list.d/bintray.rabbitmq.list /etc/apt/sources.list.d/bintray.rabbitmq.list
-COPY apt/preferences.d/erlang                 /etc/apt/preferences.d/erlang
-
-RUN apt-get update -y
-
-RUN apt-get upgrade -y && \
-    apt-get install -y rabbitmq-server
+FROM rabbitmq:3.12-management
 
 COPY docker-entrypoint.sh /
 COPY certificates/*.pem /etc/rabbitmq/