Magento 2.0.18 is the final 2.0.x release. After March 2018, Magento 2.0.x will no longer receive security patches, quality fixes, or documentation updates.
To maintain your site's performance, security, and PCI compliance, upgrade to the latest version of Magento.

Missing .gitignore files

Problem: missing .gitignore files

If you downloaded a compressed archive, there might have been missing .gitignore files that prevent the upgrade from completing properly. To apply our update, patch magento/magento-composer-installer then run composer update from your Magento installation directory.

The following figure shows an example of this issue when using the Setup Wizard.

Solution

To solve this issue:

  1. Log in to your Magento server as the Magento file system owner.
  2. Change to your Magento installation directory.
  3. Run the following commands in the order shown:

    composer update magento/magento-composer-installer
    composer update
    
  4. Try your upgrade again.