Fix the position of closing tag </li>

This closing tag was missing, then introduced in 91de91ede36c0fa4c9ddbc5961aa0e795f7b9dbb, but to a wrong position. In this way, only a category *with* children cats will have this tag.
The patch fixes this problem.
Merge pull request #25 from dujiulun/patch-1

Fix the position of closing tag </li>