Add missing import paths in template

Signed-off-by: Gavin Zhao <git@gzgz.dev>

Author: GZGavinZhao

angular_gallery/lib/builder/template/gallery.dart.mustache

@@ -5,7 +5,7 @@ import 'package:angular_router/angular_router.dart';
 import 'package:angular_forms/angular_forms.dart';
 import 'package:quiver/collection.dart';
 import 'package:angular_components/app_layout/material_persistent_drawer.dart';
-import 'package:angular_components/content/deferred_content.dart';
+import 'package:angular_components/content.dart';
 import 'package:angular_components/focus/focus.dart';
 import 'package:angular_components/focus/focus_item.dart';
 import 'package:angular_components/focus/focus_list.dart';