Fix `license` metadata

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

Thanks! 🙏

README.md

@@ -1,8 +1,8 @@
 ---
 annotations_creators: []
 language_creators: [machine-generated]
-languages: ['ca', 'de']
-licenses: ['cc-by-4.0']
+language: ['ca', 'de']
+license: ['cc-by-4.0']
 multilinguality:
 - translation
 pretty_name: 'Catalan-German aligned corpora to train NMT systems.'