[BUG] - Format EF as Personnummer

[Johannestegner]

Context

Enskild Firma should make use of the + separator in formatting if the firma/owner is above 100 years old.

The following snippet should be changed:

    public function format(bool $separator = true): string
    {
        $number = $this->getShortString();
        return $separator ? sprintf('%s-%s', substr($number, 0, 6), substr($number, 6)) : $number;
    }

Expected outcome

EF's with age over 100 should contain the + separator if separator param is true.

Actual outcome

EF's with age over 100 contains the - separator if separator param is true.

For more context, see: organisationsnummer/csharp#38