Fix `license` metadata

We recently updated the datasets metadata for consistency with other repo types (models & spaces)

Thanks! 🙏

README.md

@@ -3,10 +3,10 @@ annotations_creators:
 - no-annotation
 language_creators:
 - found
-languages:
+language:
 - da
 - da-bornholm
-licenses:
+license:
 - cc-by-4.0
 multilinguality:
 - monolingual