Add syntax highlighting [skip ci]

docs/guide/helper-array.md

@@ -239,6 +239,7 @@ Encoding will use application charset and could be changed via third argument.
 
 ## Merging Arrays <a name="merging-arrays"></a>
 
+```php
   /**
     * Merges two or more arrays into one recursively.
     * If each array has an element with the same string key value, the latter
@@ -253,6 +254,7 @@ Encoding will use application charset and could be changed via third argument.
     * @return array the merged array (the original arrays are not changed.)
     */
     public static function merge($a, $b)
+```
 
 
 ## Converting Objects to Arrays <a name="converting-objects-to-arrays"></a>