Displays the release date of the detected WP version

app/views/json/wp_version/version.erb

@@ -1,6 +1,7 @@
 <% if @version -%>
 "version": {
   "number": <%= @version.number.to_json %>,
+  "release_date": <%= @version.release_date.to_json %>,
   <%= render('@finding', item: @version) -%>
 },
 <% else -%>