Allow extending Monolog\Logger::$logLevels

src/Monolog/Formatter/HtmlFormatter.php

@@ -24,7 +24,7 @@ class HtmlFormatter extends NormalizerFormatter
     /**
      * Translates Monolog log levels to html color priorities.
      */
-    private $logLevels = array(
+    protected $logLevels = array(
         Logger::DEBUG     => '#cccccc',
         Logger::INFO      => '#468847',
         Logger::NOTICE    => '#3a87ad',