Add support for Bazaar about docker-flarum

[pojntfx]

Using the following command, I was able to install bazar and then install extensions with it from the admin panel (it showed errors while installing them, but they worked flawlessly anyways) from inside the container:

sh -c "cd /flarum/app; composer require flagrow/bazaar;"

My docker-compose:

version: "3"

services:
  web:
    image: mondedie/docker-flarum:0.1.0-beta.7.1-stable
    ports:
      - "8888:8888"
    environment:
      - FORUM_URL=http://192.168.178.44
      - DB_PASS=YOUR_PASSWORD_HERE
      - DEBUG=true
    networks:
      - opensdcp-forum
    volumes:
      - opensdcp-forum-web-assets-data:/flarum/app/assets
      - opensdcp-forum-web-extensions-data:/flarum/app/extensions
    depends_on:
      - db

  db:
    image: mariadb:10.1
    environment:
      - MYSQL_ROOT_PASSWORD=YOUR_PASSWORD_HERE
      - MYSQL_DATABASE=flarum
      - MYSQL_USER=YOUR_USERNAME_HERE
      - MYSQL_PASSWORD=YOUR_PASSWORD_HERE
    networks:
      - opensdcp-forum
    volumes:
      - opensdcp-forum-db-data:/var/lib/mysql

networks: 
  opensdcp-forum:

volumes: 
  opensdcp-forum-web-assets-data:
  opensdcp-forum-web-extensions-data:
  opensdcp-forum-db-data:

[hardware]

It does not work for me, even with your method. You don't have any of this errors : extiverse/bazaar#110 ?

Another docker mystery I suppose...