Yandex ping broken

I think it's broken. I get this

```
<html>
  <head><title>301 Moved Permanently</title></head>
  <body bgcolor="white">
    <center><h1>301 Moved Permanently</h1></center>
    <hr><center>nginx/1.2.1</center>
  </body>
</html>
```

after the request in `sitemap/ping.rb`

```
Net::HTTP.get(URI.parse(request))
```

I would have submited a PR with the new url, but couldn't find it :|
