Fix missing QA selector in note_form.vue

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22985
was merged 3 hours ago, but the CE->EE merge in
04a8d3aa dropped the changes in EE because of conflicts.

Restore this selector so master is no longer broken.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/9033

app/assets/javascripts/notes/components/note_form.vue

@@ -276,7 +276,7 @@ export default {
           <button
             :disabled="isDisabled"
             type="button"
-            class="js-vue-issue-save btn btn-success js-comment-button"
+            class="js-vue-issue-save btn btn-success js-comment-button qa-reply-comment-button"
             @click="handleUpdate();"
           >
             {{ saveButtonTitle }}