Update dependencies

[tvdijen]

Fix error+warning on PHP7.2; I couldn't get composer to run without these changes.

Got error 'PHP message: PHP Warning: count(): Parameter must be an array or an object that implements Countable in /apps/programs/StepUp-SelfService/Stepup-SelfService-2.9.0/vendor/symfony/monolog-bundle/DependencyInjection/Configuration.php on line 628

PHP message: PHP Fatal error: Uncaught Symfony\Component\Debug\Exception\ClassNotFoundException: Attempted to load class "Twig_Function_Node" from namespace "Twig".\nDid you forget a "use" statement for another namespace? in /apps/programs/StepUp-SelfService/Stepup-SelfService-2.9.0/vendor/mopa/bootstrap-bundle/Mopa/Bundle/BootstrapBundle/Twig/FormExtension.php:32

[tvdijen]

Nope, this breaks the GUI and it's not gonna be an easy fix....
I've fixed this for myself by adding...

"config": {
    "platform": {
        "php": "5.6"
    }
}

...to the composer.json file.