Fix incorrect module imports.

When importing modules with use statements, they always require the
fully qualified module name. Iow, there's no need to prefix them with an
extra backslash.

Ref: https://www.php.net/manual/en/language.namespaces.importing.php

include/help.php

@@ -1,6 +1,6 @@
 <?php
 
-use \Michelf\MarkdownExtra;
+use Michelf\MarkdownExtra;
 use CommerceGuys\Intl\Language\LanguageRepository;
 
 require_once('include/items.php');