Use inner dns for runner

docker-compose.yml

@@ -19,7 +19,7 @@ services:
       - /var/run/docker.sock:/var/run/docker.sock
     environment:
       - DRONE_RPC_PROTO=http
-      - DRONE_RPC_HOST=${HOST}
+      - DRONE_RPC_HOST=drone-server:8080
       - DRONE_RPC_SECRET=${SECRET}
       - DRONE_RUNNER_CAPACITY=2
       - DRONE_RUNNER_NAME=self-host