Fix #81266: mkdir calls directories folders in example code

reference/filesystem/functions/mkdir.xml

@@ -111,14 +111,14 @@ mkdir("/path/to/my/dir", 0700);
     <programlisting role="php">
 <![CDATA[
 <?php
-// Desired folder structure
+// Desired directory structure
 $structure = './depth1/depth2/depth3/';
 
 // To create the nested structure, the $recursive parameter 
 // to mkdir() must be specified.
 
 if (!mkdir($structure, 0777, true)) {
-    die('Failed to create folders...');
+    die('Failed to create directories...');
 }
 
 // ...