Fix `license` metadata

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

Thanks! 🙏

README.md

@@ -3,8 +3,8 @@ annotations_creators:
 - machine-generated
 language_creators:
 - found
-languages: []
-licenses:
+language: []
+license:
 - cc-by-4.0
 multilinguality:
 - monolingual