Don't hardcode the server's hostname

This fixes a usability bug where the server is run inside of a Docker container (and probably also when inside of VM?). Since the container is run on a different IP the server wouldn't listen to any incoming requests.

This does come with the downside that the server will now accept connections on any IP address.

In case anyone is interested, this is the docker-compose.yml file that I'm using to install and serve my slides:

version: '2'

services:
  npm:
    image: node:6
    volumes:
      - .:/usr/src/app
    working_dir: /usr/src/app
    ports:
      - "3000:3000"
    command: [npm, run, start]

FormidableLabs / spectacle-boilerplate

Don't hardcode the server's hostname #35