Update German Bert model card
We changed the vocab to work with run_split_on_punc tokenization.
Now there are much less [UNK] punctuation tokens.

For more details see deepset-ai/FARM/issues/60
@Timoeller @tholor LGTM and thanks for linking to the discussion on the FARM repo. 👍<|||||>cherry-picked only the relevant change in 4ab8ab4f50baf391612cbc78cfa3f09b7ad0c3ac