Fix sitemaps loc of subdirectories

Auto-generated sitemap.xml is wrong when using subdirectories.

wrong:

```xml
<url>
    <loc>http://www.example.com/foo.html</loc>
    <lastmod>2014-05-04T04:14:22Z</lastmod>
</url>
```

expect:

```xml
<url>
    <loc>http://www.example.com/bar/foo.html</loc>
    <lastmod>2014-05-04T04:14:22Z</lastmod>
</url>
```

I fixed the above issue.