This feature was removed in May 2017.
The automatic update script was removed in May 2017 due to massive bugs in Joomla! 3.7. These bugs broke all CLI scripts which make direct or indirect use of the JSession package, including simply checking if a user is logged in. This includes the update script. It cannot be fixed because the update script uses the core JUpdater and JInstaller APIs to fetch and install updates. Both of them use JSession which means they cannot be used from a CLI script.
The only thing we can do is remove a feature which can no longer work because Joomla! broke backwards compatibility with itself.