Update docblock for getShared method

Author: hailwood

src/Inertia.php

@@ -7,7 +7,7 @@
 /**
  * @method static void setRootView($name)
  * @method static void share($key, $value = null)
- * @method static array getShared($key = null)
+ * @method static array getShared($key = null, $default = null)
  * @method static void version($version)
  * @method static int|string getVersion()
  * @method static \Inertia\Response render($component, $props = [])