Composer

Please always make sure composer.lock file is updated after any changes in composer.json file. You can use composer update command to update any package, in this case composer will take care about updating of composer.lock file.

composer update drupal/metatag

Also you can use composer update --lock command to force updating of composer.lock file according to dependencies in composer.json.

Please check official composer documentation for details: https://getcomposer.org/doc/01-basic-usage.md