Merge branch '2.x' into 3.x

* 2.x:
  Update markdown-to-html converter missing message
  Fix CS
  Missing Environment and LoaderInterface

extra/markdown-extra/DefaultMarkdown.php

@@ -28,7 +28,7 @@ public function __construct()
         } elseif (class_exists(Parsedown::class)) {
             $this->converter = new ErusevMarkdown();
         } else {
-            throw new \LogicException('You cannot use the "markdown_to_html" filter as no Markdown library is available; try running "composer require league/html-to-markdown".');
+            throw new \LogicException('You cannot use the "markdown_to_html" filter as no Markdown library is available; try running "composer require league/commonmark".');
         }
     }