fix error in carrier: DHL Germany

```
Carrier: DHL Germany
Line: 43

**ERROR**

$link = 'http://nolp.dhl.de/nextt-online-public/set_identcodes.do?lang=de&idc=' 
. $this->trackingNumber;

**FIX**

$link = 'http://nolp.dhl.de/nextt-online-public/set_identcodes.do?lang=de&idc=' 
. $trackingNumber;
```

Original issue reported on code.google.com by `gerdchri...@googlemail.com` on 30 Jan 2013 at 9:05
