Node with support for headless WebGL

To run headless WebGL tests under Docker with gl, #stackgl's fork of headless-gl, you'll need:

node
OpenGL drivers
A headless back buffer with OpenGL support

This image contains:

The latest node 6 LTS, because it's FROM node:6
The packages required for gl use under Travis, including xvfb
Yelp's dumb-init to handle the PID 1 duties xvfb-run won't

The full process tree will be:

dumb-init
- xvfb-run
  - xvbf
  - node, or whatever else you put in your CMD

I've left out gl itself. If you want it globally installed in your derived image, add these lines to your Dockerfile:

FROM garthk/node-for-headless-webgl
ENV NODE_PATH /usr/local/lib/node_modules
RUN npm install --unsafe-perm --global gl