NishThakkar

It looks like the problem is that [merge](https://github.com/knadh/koanf/blob/master/koanf.go#L429) acquired a write lock prior to calling the [custom merge function](https://github.com/knadh/koanf/blob/master/koanf.go#L434). Since the custom merge function calls k.String("env"), which eventually calls [Get](https://github.com/knadh/koanf/blob/master/koanf.go#L336),...