updated _config.php from calling Object to DataObject to comply with php 7.3

Author: callan-stretton

_config.php

@@ -7,7 +7,7 @@
 LeftAndMain::require_css(MODULE_MANAGER_DIR . '/css/cms.css');
 
 // add functionality to SiteTree
-Object::add_extension('SiteTree', 'ModuleSiteTreeExtension');
+DataObject::add_extension('SiteTree', 'ModuleSiteTreeExtension');
 
 CMSMenu::remove_menu_item('ModuleManagerAddController');
 CMSMenu::remove_menu_item('ModuleManagerEditController');