Fails if link is defined in compose.yml

[andrewsanchez]

https://github.com/fnichol/docker-ngrok/blob/338760aaf2a3af2deea64c8822db92cc10e404c9/ngrok_discover#L13-L18

version: "3.7"
services:

  listener:
    image: listener
    build:
      context: ./listener
    ports:
      - "5000:80"
    volumes:
      - "/Users/asanchez122/Projects/webhook-listener/data:/app/data"

  tunnel:
    image: fnichol/ngrok
    ports:
      - "3270:4040"
    links:
      - "listener:http"

Adding this to compose.yml fixed the issue:

    environment:
      HTTP_PORT: 4040