Avoid usint `cursor.snapshot()` in preparation for MongoDB version upgrade

CHANGES.md

@@ -4,6 +4,7 @@
 
 * Feature: Create/edit linker with GUI
 * Improvement: Paging page histories
+* Improvement: Avoid usint `cursor.snapshot()` in preparation for MongoDB version upgrade
 * Fix: To be able to delete attachment metadata even when the actual data does not exist
 * Fix: Limit the attrubutes of user data for `/_api/v3/users`
 * Upgrade libs

src/server/service/export.js

@@ -167,7 +167,7 @@ class ExportService {
 
     const nativeCursor = collection.find();
     const readStream = nativeCursor
-      .snapshot()
+      .lean()
       .stream({ transform: JSON.stringify });
 
     // get TransformStream

src/server/service/search-delegator/elasticsearch.js

@@ -378,7 +378,6 @@ class ElasticsearchDelegator {
         { path: 'creator', model: 'User', select: 'username' },
         { path: 'revision', model: 'Revision', select: 'body' },
       ])
-      .snapshot()
       .lean()
       .cursor();