Fix typo in json field name attachements to attachments
Fix typo in json field name attachements to attachments

In the ttrss api client was a typo for the attachments field name,
so the attachments wasn't gathered correctly.

Fixes #177

der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat