Fix `license` metadata

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

Thanks! 🙏

README.md

@@ -2,9 +2,9 @@
 annotations_creators: []
 language_creators:
 - crowdsourced
-languages:
+language:
 - si
-licenses:
+license:
 - mit
 multilinguality:
 - monolingual