[Tails-l10n] (review)[de] unfuzzy and fix news page

Hi,

the link to subscribe to the amnesia-news mailing list was changed in
the English original. I changed the German version accordingly and
unfuzzied the string. The translation itself did not change, just the
URL/markdown link.

Please review:

https://gitlab.com/flapflap/tails.git
branch: de_news
HEAD commit: 2233d69b - unfuzzy & fix string

Cheers,
~flapflap