fix typo that was preventing description from saving on cards (fixes #2151)

frontend/src/components/SaveQuestionModal.jsx

@@ -85,7 +85,7 @@ export default class SaveQuestionModal extends Component {
 
         card.name = details.name.trim();
         // since description is optional, it can be null, so check for a description before trimming it
-        card.details = details.description ? details.description.trim() : null;
+        card.description = details.description ? details.description.trim() : null;
         card.public_perms = 2; // public read/write
 
         if (details.saveType === "create") {