Convert string references to ::class

PHP 5.5.9 adds the new static `class` property which provides the fully qualified class name. This is preferred over using strings for class names since the `class` property references are checked by PHP.

config/mary.php

@@ -40,7 +40,7 @@ return [
      */
     'components' => [
         'spotlight' => [
-            'class' => 'App\Support\Spotlight',
+            'class' => App\Support\Spotlight::class,
         ],
     ],
 ];