Replaced deprecated OR operator https://getcomposer.org/doc/articles/versions.md#version-range

Added 5.8.* compatibility
Updated dependency versions
Added phpunit result cache to gitignore

src/CartItem.php

@@ -379,6 +379,13 @@ class CartItem implements Arrayable, Jsonable
 
                 return;
 
+            case 'modelFQCN':
+                if (isset($this->associatedModel)) {
+                    return $this->associatedModel;
+                }
+
+                return;
+
             default:
                 return;
         }