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