Fix `license` metadata

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

Thanks! 🙏

README.md

@@ -6,7 +6,7 @@ annotations_creators:
 language_creators:
 - crowdsourced
 - expert-generated
-languages:
+language:
 - en
 - en-GB
 - en-US
@@ -22,7 +22,7 @@ languages:
 - cs
 - ko
 - zh
-licenses:
+license:
 - cc-by-4.0
 multilinguality:
 - multilingual