Documentation Error - connectionFactory should be connectionfactory

In the documentation describing exchanges, the DSL reads:

```
rabbitmq {
    connectionFactory {
        ...
    }
    queues = {
        exchange name: 'my.topic', type: topic
    }
}
```

Note the capital F in factory. 

When running this, the application shows an error:

```
[localhost-startStop-1] ERROR RabbitmqGrailsPlugin  - RabbitMQ connection factory settings (rabbitmq.connectionfactory.username, rabbitmq.connectionfactory.password and rabbitmq.connectionfactory.hostname) must be defined in Config.groovy

```

The attached patch fixes this error in the documentation.