Fix `license` metadata

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

Thanks! 🙏

README.md

@@ -2,10 +2,10 @@
 annotations_creators:
 - machine-generated
 language_creators: []
-languages:
+language:
 - fr-FR
 - fr
-licenses:
+license:
 - wtfpl
 multilinguality:
 - monolingual