Seems like the post() method of FluentLogger can not handle numeric arrays

This problem was costing me some time to find that only string indicies in the array are allowed:

```
/**
* send a message to specified fluentd.
*
* @param string $tag
* @param array $data
* @return bool
*
* @api
*/
public function post($tag, array $data)
{
$entity = new Entity($tag, $data);

return $this->postImpl($entity);
}
```

I do now know the exact reason for this behaviour, but can you please just apply PHPs `strval()` function for posted arrays with numeric indicies?

If this problem does not result from the library (I am not 100% sure) please sorry for bothering the wrong implementors ;-)