Another fix for checklists item migration error "title is required"

https://github.com/wekan/wekan/commit/8d5cbf1e6c2b6d467fe1c0708cd794fd11b98a2e#commitcomment-29362180

Thanks to oec !

Closes #1576

server/migrations.js

@@ -140,7 +140,7 @@ Migrations.add('add-sort-checklists', () => {
         noValidate
       );
     }
-    checklist.items.find().forEach((item, index) => {
+    checklist.items.forEach((item, index) => {
       if (!item.hasOwnProperty('sort')) {
         Checklists.direct.update(
           { _id: checklist._id, 'items._id': item._id },