Wrong string for pt-BR locale

[lcneves]

index.js, line 102:
french: ['fr', 'tl', 'pt-br'],

Should be:
french: ['fr', 'tl', 'pt-BR'],

[ljharb]

cc @schleyfox to confirm that we don't need to keep both capitalizations

[schleyfox]

I don't think we do any handling of the locales that are passed in that would make this case insensitive, so changing the capitalization could be breaking. You'd probably need both capitalizations.