Refactor dashboard milestone show inside dispatcher

app/assets/javascripts/dispatcher.js

@@ -196,10 +196,14 @@ import Activities from './activities';
           break;
         case 'projects:milestones:show':
         case 'groups:milestones:show':
-        case 'dashboard:milestones:show':
           new Milestone();
           new Sidebar();
           break;
+        case 'dashboard:milestones:show':
+          import('./pages/dashboard/milestones/show')
+            .then(callDefault)
+            .catch(fail);
+          break;
         case 'dashboard:issues':
         case 'dashboard:merge_requests':
           projectSelect();

app/assets/javascripts/pages/dashboard/milestones/show/index.js

+import Milestone from '~/milestone';
+import Sidebar from '~/right_sidebar';
+
+export default () => {
+  new Milestone(); // eslint-disable-line no-new
+  new Sidebar(); // eslint-disable-line no-new
+};