Fix checkOrFixLastRevs in https://s.apache.org/oak-mongo.js

The oak-mongo.js 's checkOrFixLastRevs function does not check for changes applied in Oak 1.2 IIUC, which sas:

Starting with Oak 1.2 the _lastRev value for a cluster node is only updated when there is no corresponding entry in _revisions or _commitRoot. That is, when the node wasn't changed but a descendant node was added, removed or modified.