Dropbox backup error on Runway 3.1.1

After updating to Runway 3.1.1, I get the error:

PHP Parse error:  syntax error, unexpected '->' (T_OBJECT_OPERATOR) in /home/2/d/dunderverk/www/dv-cms/core/runway/apps/perch_dropbox/vendor/tightenco/collect/src/Collect/Support/Collection.php on line 155

Which refers to this part of that file:

        $values = (isset($key) ? $this->pluck($key) : $this)
                    ->sort()->values();

Anyone else experiencing this issue, or have any idea on how to solve it?

Worked perfectly until the latest update.

Diagnostics:
Perch Runway: 3.1.1, PHP: 7.0.27-0+deb9u1, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: b5c5906d452ec590732a93b051f3827e02749b83 $, with PDO
Server OS: Linux, cgi-fcgi
Installed apps: content (3.1.1), assets (3.1.1), categories (3.1.1), perch_blog (5.6.1), perch_forms (1.10), perch_shop_orders (1.2.5), perch_shop_products (1.2.5), perch_shop (1.2.5), perch_members (1.6.2), redfinch_logger (1.0.1)
App runtimes: <?php $apps_list = [ 'perch_forms', 'perch_blog', 'perch_members', 'perch_shop', ];
Image manipulation: GD Imagick
PHP limits: Max upload 128M, Max POST 128M, Memory: 129M, Total max file upload: 128M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes