Add dependencies to docker image

I've been following the documentation (Running under Docker : Node-RED) but can't figure it out. It builds but when I try to open 127.0.0.1:1880 I get ERR_CONNECTION_REFUSED in Chrome, so the web service is not running?

What I wanted to do is add support for Elasticsearch with the package from Jeff, this is my Dockerfile:

FROM nodered/node-red:latest
USER root
RUN npm install node-red-contrib-elasticsearch-jd
USER node-red

Build it:

docker build -t test/noderedext:latest .

Run it:

docker run test/noderedext -p 1880:1880 -d

I know I'm not mounting any volumes her, so I will get the warning up on the dashboard but for now I only want to add the dependency before I go ahead and complete the container.