Fix `license` metadata

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

Thanks! 🙏

README.md

@@ -4,7 +4,7 @@ annotations_creators:
 - expert-generated
 language_creators:
 - found
-languages:
+language:
 - en
 - it
 - vi
@@ -12,7 +12,7 @@ languages:
 - uk
 - tr
 - ar
-licenses:
+license:
 - gpl-3.0
 multilinguality:
 - translation