MDL-58548 lib: Update htmlpurifier to the latest version.

lib/htmlpurifier/HTMLPurifier/Config.php

@@ -21,7 +21,7 @@ class HTMLPurifier_Config
      * HTML Purifier's version
      * @type string
      */
-    public $version = '4.8.0';
+    public $version = '4.9.3';
 
     /**
      * Whether or not to automatically finalize
@@ -333,7 +333,7 @@ class HTMLPurifier_Config
         }
 
         // Raw type might be negative when using the fully optimized form
-        // of stdclass, which indicates allow_null == true
+        // of stdClass, which indicates allow_null == true
         $rtype = is_int($def) ? $def : $def->type;
         if ($rtype < 0) {
             $type = -$rtype;