Using [] is deprecated

V performance helperu: orm\Repository\Helpers\PerformanceHelper.php:58  

``` php
$key = $key ? $key : '*';
               if (strlen($key) > 50)
              {
                   $key = substr($key, 0, 20) . md5($key);
              }
             self::$toLoad = isset($cache[$key]) ? $cache[$key] : NULL;
```

Hlásí:
Using [] is deprecated; use Cache::load(key) !== NULL instead.
