Handelsregister demo code returns error

Running the demo code in the README.md for the Handelsregister module returns an error.

How to reproduce:
```
>>> from deutschland import Bundesanzeiger
>>> from deutschland import Handelsregister
>>> hr = Handelsregister()
>>> hr.search(keywords="Deutsche Bahn Aktiengesellschaft")
```

Expected result:
* Handelsregister infos to be retrieved and stored in 'hr' object.

What I got instead:
```
Traceback (most recent call last):
File "", line 1, in
File "/home/xxx/Dokumente/bundesapi/test_bundesapi_2/env/lib/python3.9/site-packages/deutschland/handelsregister/handelsregister.py", line 138, in search
return self.search_with_raw_params(params)
File "/home/xxx/Dokumente/bundesapi/test_bundesapi_2/env/lib/python3.9/site-packages/deutschland/handelsregister/handelsregister.py", line 215, in search_with_raw_params
return self.__find_entries(soup)
File "/home/xxx/Dokumente/bundesapi/test_bundesapi_2/env/lib/python3.9/site-packages/deutschland/handelsregister/handelsregister.py", line 242, in __find_entries
data = self.__extract_history(tr)
File "/home/xxx/Dokumente/bundesapi/test_bundesapi_2/env/lib/python3.9/site-packages/deutschland/handelsregister/handelsregister.py", line 276, in __extract_history
[position, historical_name] = tds[1].text.strip().split(".) ", 1)
ValueError: not enough values to unpack (expected 2, got 1)
```

My env:
* Ubuntu 20.04, venv with 3.9.6 and pip 21.2.4