Fix `license` metadata

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

Thanks! 🙏

README.md

@@ -1,10 +1,10 @@
 ---
 annotations_creators: []
 language_creators: []
-languages:
+language:
 - si
 - en
-licenses: [mit]
+license: [mit]
 multilinguality:
 - multilingual
 pretty_name: ''