Fix markup in HtmlHelper doc block.

This will help the API generate correctly.

src/View/Helper/HtmlHelper.php

@@ -416,7 +416,7 @@ public function link($title, $url = null, array $options = [])
      *   CSS stylesheets. If `$path` is prefixed with '/', the path will be relative to the webroot
      *   of your application. Otherwise, the path will be relative to your CSS path, usually webroot/css.
      * @param array $options Array of options and HTML arguments.
-     * @return string CSS <link /> or <style /> tag, depending on the type of link.
+     * @return string CSS `<link />` or `<style />` tag, depending on the type of link.
      * @link http://book.cakephp.org/3.0/en/views/helpers/html.html#linking-to-css-files
      */
     public function css($path, array $options = [])