Version prerequisites and updated docker-compose file to run this repo

[KunalArora]

Following are the version prerequisites to run this repo, along with the updated docker-compose.yml file.

docker version => 20.10.8, build 3967b7d
docker-compose version => 1.27.4, build unknown
airflow version => 2.1.3

Updated docker-compose.yml file:

version: '3'
services:
  postgres:
    image: postgres:9.6
    environment:
      - POSTGRES_USER=airflow
      - POSTGRES_PASSWORD=airflow
      - POSTGRES_DB=airflow
    ports:
      - "5432:5432"

  webserver:
    image: puckel/docker-airflow:1.10.9
    build:
      context: https://github.com/puckel/docker-airflow.git#1.10.9
      dockerfile: Dockerfile
      args:
        AIRFLOW_DEPS: gcp_api,s3
        PYTHON_DEPS: sqlalchemy==1.3.0
    restart: always
    depends_on:
      - postgres
    environment:
      - LOAD_EX=n
      - EXECUTOR=Local
      - FERNET_KEY=jsDPRErfv8Z_eVTnGfF8ywd19j4pyqE3NpdUBA_oRTo=
    volumes:
      - ./examples/intro-example/dags:/usr/local/airflow/dags
      # Uncomment to include custom plugins
      # - ./plugins:/usr/local/airflow/plugins
    ports:
      - "8080:8080"
    command: webserver
    healthcheck:
      test: ["CMD-SHELL", "[ -f /usr/local/airflow/airflow-webserver.pid ]"]
      interval: 30s
      timeout: 30s
      retries: 3