Update to German translation

I couldn’t find the plugin in https://plugins.trac.www.ads-software.com/newticket,
so I post here.

The tranlation of msgid ” and ” in

co-authors-plus/languages/co-authors-plus-de_DE.po

should be ” und ” with the whitespaces, the same way it is in French and English.

https://www.ads-software.com/extend/plugins/co-authors-plus/