Fixing PHPdoc referencing session driver

I think this is a copy/paste from https://github.com/laravel/framework/blob/e6c8aa0e39d8f91068ad1c299546536e9f25ef63/src/Illuminate/Session/SessionManager.php#L204 and is not meant to say `session` but rather `Scout`.

src/EngineManager.php

@@ -68,7 +68,7 @@ public function createNullDriver()
     }
 
     /**
-     * Get the default session driver name.
+     * Get the default Scout driver name.
      *
      * @return string
      */