Updated all dependencies and prepared for PHP 8

RoboFile.php

@@ -1,7 +1,8 @@
 <?php
 
 use Symfony\Component\Finder\Finder;
-use CloudObjects\SDK\COIDParser, CloudObjects\SDK\ObjectRetriever;
+use CloudObjects\SDK\COIDParser, CloudObjects\SDK\ObjectRetriever,
+    CloudObjects\SDK\Constants;
 use Webmozart\Assert\Assert;
 
 /**
@@ -182,7 +183,7 @@ class RoboFile extends \Robo\Tasks {
             
         $this->taskWriteToFile($stackDir.'/meta.json')
             ->text(json_encode([
-                'rev' => $stackObject->getProperty(ObjectRetriever::REVISION_PROPERTY)->getValue(),
+                'rev' => $stackObject->getProperty(Constants::PROPERTY_REVISION)->getValue(),
                 'whitelisted_classes' => $whitelistedClasses
             ]))
             ->run();