ILM example config has colons instead of =>

ILM beta documentation has typos in the example config.  The colon notation should be =>

```
output {
  elasticsearch {
    ilm_enabled => true
    ilm_rollover_alias: "custom"
    ilm_pattern: "000001"
    ilm_policy: "custom_policy"
  }
}
```

https://www.elastic.co/guide/en/logstash/current/plugins-outputs-elasticsearch.html#plugins-outputs-elasticsearch-ilm