Fix typo causing a Sphinx warning

Author: LittleJ

user_guide_src/source/general/ajax.rst

@@ -31,7 +31,9 @@ For libraries like jQuery for example, it is not necessary to make explicit the
 
     $.ajax({
         url: "your url",
+
         headers: {'X-Requested-With': 'XMLHttpRequest'}
+
     });