fix(ParsedownExtra): update namespace

lib/Pico.php

@@ -42,6 +42,10 @@
  * @license http://opensource.org/licenses/MIT The MIT License
  * @version 3.0
  */
+
+use Erusev\Parsedown\Parsedown;
+use Erusev\ParsedownExtra\ParsedownExtra;
+
 class Pico
 {
     /**
@@ -1561,7 +1565,7 @@ class Pico
     public function getParsedown()
     {
         if ($this->parsedown === null) {
-            $className = $this->config['content_config']['extra'] ? 'ParsedownExtra' : 'Parsedown';
+            $className = $this->config['content_config']['extra'] ? ParsedownExtra::class : Parsedown::class;
             $this->parsedown = new $className();
 
             $this->parsedown->setBreaksEnabled((bool) $this->config['content_config']['breaks']);