sk.po: Language sk_SK → sk
sk.po: Language sk_SK → sk

Because i18nspector tells me to do so:
https://travis-ci.org/newsboat/newsboat/jobs/321420050#L337

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