title: PHP Monolog logger RotatingFileHandler never rotates files
body: <p>PHP 7.1, ubuntu 12.04 LTS, monolog version is 1.23.0.</p>
  
  <p>Logger initialisation:</p>
  
  <pre><code>&lt;?php
      $logger = new Logger('app');
      $logger-&gt;pushHandler(
          new RotatingFileHandler(
              Main\Application::getDocumentRoot() . '/runtime/logs/app.log',
              5,
              Logger::DEBUG
          )
      );
  </code></pre>
  
  <p>Currently there is 24 log files in the path, not 5 as expected.</p>
  
  <p>How to force monolog to rotate files as expected? Do I need do some extra steps to rotate files, what reason may cause not deleting old logs?</p>