Fix mongodb move file operation

Author: shiling

src/main/java/picoded/dstack/mongodb/MongoDB_FileWorkspaceMap.java

@@ -726,7 +726,7 @@ public void backend_moveFile(String oid, String sourceFile, String destinationFi
 		Bson query = Filters.eq("filename", sourceFullPath);
 		Bson update = new Document("$set", new Document("filename", destinationFullPath));
 
-		filesCollection.updateOne(query, update, null);
+		filesCollection.updateOne(query, update);
 
 	}