Union types are only allowed since php8

[chengshanmu]

syntax error, unexpected '|', expecting ';' or '{',
\vendor\facebook\php-business-sdk\src\FacebookAds\Cursor.php,438

public function current() : AbstractObject|bool {

[natewiebe13]

See: #572 (comment)

Since then, composer.json has been updated with php >=8 as a version constraint, so this is correct.

[chengshanmu]

thanks