Fix pg migration in Dockerfile

[altafan]

Closes #93.

The bug has been introduced in dd0b884bcfa26defd84d5c2b1d7c254156d60d5b.

Please @tiero @louisinger review this.

[altafan]

you can use the following compose file to test this out:

version: "3.7"

services:
  oceand:
    container_name: oceand
    build: 
      context: .
      dockerfile: Dockerfile
    restart: unless-stopped
    environment:
      - OCEAN_LOG_LEVEL=5
      - OCEAN_NO_TLS=true
      - OCEAN_NO_PROFILER=true
      - OCEAN_ELECTRUM_URL=ssl://blockstream.info:465
      - OCEAN_NETWORK=testnet
      - OCEAN_UTXO_EXPIRY_DURATION_IN_SECONDS=60
      - OCEAN_DB_HOST=oceand-db
      - OCEAN_DB_NAME=oceand-db
      - OCEAN_DB_PASSOWRD=secret
    ports:
      - "18000:18000"
  oceand-db:
    container_name: oceand-db
    image: postgres
    restart: unless-stopped
    environment:
      - POSTGRES_USER=root
      - POSTGRES_PASSWORD=secret
      - POSTGRES_DB=oceand-db
    ports:
      - "5432:5432"

[louisinger]

tACK