Set noteableType on noteableData as provided from DOM dataset

app/assets/javascripts/mr_notes/index.js

@@ -13,8 +13,11 @@ export default function initMrNotes() {
     data() {
       const notesDataset = document.getElementById('js-vue-mr-discussions')
         .dataset;
+      const noteableData = JSON.parse(notesDataset.noteableData);
+      noteableData.noteableType = notesDataset.noteableType;
+
       return {
-        noteableData: JSON.parse(notesDataset.noteableData),
+        noteableData,
         currentUserData: JSON.parse(notesDataset.currentUserData),
         notesData: JSON.parse(notesDataset.notesData),
       };