fix env.example, add db hostname

.env.example

@@ -1,5 +1,5 @@
 DOCKER_PROJECT_NAME=myapp
-DOCKER_HOST=app.local
+DOCKER_HOSTNAME=app.local
 DOCKER_HTTP_PORT=8080
 DOCKER_MYSQL_PORT=3306
 DOCKER_REDIS_PORT=6379

docker-compose.yml

@@ -53,6 +53,7 @@ services:
   db:
     image: mysql:latest
     command: --default-authentication-plugin=mysql_native_password
+    hostname: ${DOCKER_PROJECT_NAME}-db}
     environment:
       MYSQL_ROOT_USER: root
       MYSQL_ALLOW_EMPTY_PASSWORD: "true"