Typo fix @ thunder_updater

After update Drupal I was got this error:

$ drush cr
<em class="placeholder">Warning</em>: Declaration of Drupal\thunder_updater\ReversibleConfigDiffer::format($config, $prefix = '') should be compatible with Drupal\config_update\ConfigDiffer::format(array $config, $prefix = '') in <em class="placeholder">include()</em> (line <em class="placeholder">440</em> of <em class="placeholder">phar:///usr/local/bin/drush/vendor/composer/ClassLoader.php</em>). <pre class="backtrace">include() (Line: 440)
Composer\Autoload\includeFile(&#039;/Users/michal.landsman/localhost/marianne-thunder/docroot/profiles/contrib/thunder/modules/thunder_updater/src/ReversibleConfigDiffer.php&#039;) (Line: 322)
Composer\Autoload\ClassLoader-&gt;loadClass(&#039;Drupal\thunder_updater\ReversibleConfigDiffer&#039;)
spl_autoload_call(&#039;Drupal\thunder_updater\ReversibleConfigDiffer&#039;)
ReflectionClass-&gt;__construct(&#039;Drupal\thunder_updater\ReversibleConfigDiffer&#039;) (Line: 73)
Drupal\webprofiler\Compiler\ServicePass-&gt;extractData(Object, Object) (Line: 26)
Drupal\webprofiler\Compiler\ServicePass-&gt;process(Object) (Line: 104)
Symfony\Component\DependencyInjection\Compiler\Compiler-&gt;compile(Object) (Line: 598)
Symfony\Component\DependencyInjection\ContainerBuilder-&gt;compile() (Line: 1299)
Drupal\Core\DrupalKernel-&gt;compileContainer() (Line: 883)
Drupal\Core\DrupalKernel-&gt;initializeContainer() (Line: 465)
Drupal\Core\DrupalKernel-&gt;boot() (Line: 708)
Drupal\Core\DrupalKernel-&gt;prepareLegacyRequest(Object) (Line: 43)
drupal_rebuild(Object, Object) (Line: 300)
drush_cache_rebuild() (Line: 422)

PHP 7.1.x