"/etc/init.d/td-agent stop" fails stoping the daemon

I'm using td-agent 1.1.11-1 on Ubuntu Server 10.04.

"/etc/init.d/td-agent stop" often fails after a long time:

```
$ time sudo /etc/init.d/td-agent stop
 * Stopping td-agent td-agent                                       [fail]

real	0m35.053s
user	0m0.320s
sys	0m0.140s
```

This patch fixes the issue because the process name of td-agent is actually "ruby", not "td-agent".

> −n, −−name process-name
> Check for processes with the name process-name (according to /proc/pid/stat).