Translation does not translate all keys

Hi

Maybe I'm misunderstanding this package :)

I have en as base, then when I execute ```php artisan translate:files``` I would assume that it would use the /lang/en.json as base and the use google translate to translate to es, fr etc.

It almost works, but.... /lang/fr.json does not contain all the keys that are in /lang/en.json

Did I miss some setup ?
 