auto-update.php

<?php

// Add this as a mu-plugin.

if ( isset( $_GET['wp_maybe_auto_update'] ) ) {
	add_filter( 'automatic_updates_is_vcs_checkout', '__return_false' );
	add_action( 'template_redirect', function() {
		$time = date( 'r' );
		echo "Starting... $time<br />";
		delete_site_option( 'auto_core_update_failed' );
		delete_option( 'auto_upgrader.lock' );
		delete_site_transient( 'update_core' );
		wp_maybe_auto_update();
		die( 'Done, check your email.' );
	} );
}