String concat code blocks were not equivalent.

If the array is empty, the "bad" code will return `<ul></ul>` and the "good" code will return `<ul><li></li></ul>`.

Although I would prefer this over the for loop:

    function inbox(messages) {
      items = messages.map(function(message) {
        return '<li>' + message.message + '</li>';
      });

      return '<ul>' + items.join('') + '</ul>';

README.md

@@ -250,10 +250,10 @@
       items = [];
 
       for (i = 0; i < length; i++) {
-        items[i] = messages[i].message;
+        items[i] = '<li>' + messages[i].message + '</li>';
       }
 
-      return '<ul><li>' + items.join('</li><li>') + '</li></ul>';
+      return '<ul>' + items.join('') + '</ul>';
     }
     ```