docker-compose.yml weirdness

So I have a docker-compose.yml that looks like this:

```
mongo:
    image: mongo:2.6
    command: "--smallfiles"
    volumes_from: data
    restart: always
    mem_limit: 100MB

data:
    image: mongo:2.6
    volumes: /data/db
```

When I run `docker-compose up`, I get this:

`Service "mongo" mounts volumes from "d", which is not the name of a service or container.`

Version: 1.1.0-rc2

Queh?
