isbn-groups.js needs to be imported manually

[Abekonge]

When imported as unstructed, only isbn-numbers belonging to the three isbn-grous included in the isbn.js file will validate (english-speaking, Japan), will work. All other isbn-numbers will fail.

The hacky fix is to include the isbn-groups.js manually. But it would be nice if the package "just worked" from the get-go.

[Abekonge]

A fork from another variant of this lib fixes this: https://github.com/AV-Forlaget/isbnjs