Clarify that JSON Toolkit supports 2019-09 and 2020-12 (#863)

Author: jviotti

data/validator-libraries-modern.yml

@@ -56,6 +56,7 @@
     - name: JSON Toolkit
       url: https://github.com/sourcemeta/jsontoolkit
       notes: Comes with its own JSON parser
+      date-draft: [2020-12, 2019-09]
       draft: [7, 6, 4]
       license: AGPL-3.0 and commercial
       last-updated: "2024-06-13"