Externalize button string

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

@@ -194,7 +194,7 @@ js-autosize markdown-area js-vue-issue-note-form js-vue-textarea"
           class="btn btn-cancel note-edit-cancel js-close-discussion-note-form"
           type="button"
           @click="cancelHandler()">
-          Discard draft
+          = {{ __('Discard draft') }}
         </button>
       </div>
     </form>