Fix: fix " `doctype 5` is deprecated " error

## Fixed a tiny error, by the way, thanks for your tutorial

### The error
![snip20140103_2](https://f.cloud.github.com/assets/3378031/1837143/a2f5c3a8-741f-11e3-8b69-10298e0629a6.png)

### After fix the error
![snip20140103_3](https://f.cloud.github.com/assets/3378031/1837144/ad10cd42-741f-11e3-83c9-aa0355050f8a.png)