Set livereload-port for docker watch to work

[airtonix]

It's be great if watch mode in docker would work.

to make this happen, you need to allow setting the live-reload port from docpress, otherwise get-port will choose a random port every time, which isn't feasible for docker-compose.

version: "2.1"

services:

  frontend:
    image: my-image-name
    ports:
      - 3000:3000
    environment:
      - PORT=3000
      - HOST=0.0.0.0
      - CHOKIDAR_USEPOLLING=true
    working_dir: /opt/app/
    command: npm run serve
    volumes:
      - ./package.json:/opt/app/package.json
      - ./docs:/opt/app/docs
      - ./README.md:/opt/app/README.md
      - /opt/app/node_modules