⬆️ 🔨 Upgrade PHP Markdown library.

The current version throws deprecated warning with PHP7.1 and PHPUnit.
Upgrade the Markdown library to the current PHP Markdown Lib 1.7.0.
Used composer to manage this library.

vendor/autoload.php

@@ -2,6 +2,6 @@
 
 // autoload.php @generated by Composer
 
-require_once __DIR__ . '/composer' . '/autoload_real.php';
+require_once __DIR__ . '/composer/autoload_real.php';
 
 return ComposerAutoloaderInit7b34d7e50a62201ec5d5e526a5b8b35d::getLoader();