Compile error for golang ECS logging

At the link https://www.elastic.co/guide/en/ecs-logging/go-zerolog/current/setup.html, I run the example code:

```
// Add custom fields.
log.Info().Msg("hello world").Str("custom", "foo")
```

it gives me the following error:

`log.Info().Msg("hello world") (no value) used as value or type`

I need to change it to:

`log.Info().Str("custom", "foo").Msg("Hello, World!")
`
to make it work by referring https://github.com/rs/zerolog