ERROR: Version in "./docker-compose.dual.yml" is unsupported

[chakpongchung]

pangolins:keras-serving$ ./start-dual-servers.sh
ERROR: Version in "./docker-compose.dual.yml" is unsupported. You might be seeing this error because you're using the wrong Compose file version. Either specify a version of "2" (or "2.0") and place your service definitions under the services key, or omit the version key and place your service definitions at the root of the file to use version 1.
For more on the Compose file format versions, see https://docs.docker.com/compose/compose-file/