Got response code 400 when receive unsubscribe request

I tried to request unsubscribe by https://pubsubhubbub.appspot.com/subscribe

And, I saw followings message.

```
==> /service/my-pubsubhubbub/log/main/current <==
@40000000519c2c830659fbf4 ERROR: hub.lease_seconds is missing
@40000000519c2c83065a07ac 8.35.201.160 - - [22/May/2013:11:24:57 +0900] "GET /subscriber?hub.topic=http://blog.livedoor.jp/ytnobody/atom.xml&hub.challenge=14461605901000989736&hub.mode=unsubscribe HTTP/1.0" 400 28 "-" "AppEngine-Google; (+http://code.google.com/appengine; appid: s~pubsubhubbub-hrd)" 5092
```

Afterward, I fixed this issue that's in your clever module.
Please check it.

Best regards.