Updated to the latest version and getting PHP errors

I'm upgrading from 23.4.12651 to 23.6.12860.  I run 'svn update' in /opt/observium.  When I try to run 'discovery -u' I get the following:

Updated to revision 12863.
root@observium1:/opt/observium# ./discovery.php -u
PHP Parse error:  syntax error, unexpected '=' in /opt/observium/includes/observium.inc.php on line 427

This is running on: 

PRETTY_NAME="Ubuntu 18.04.6 LTS"

Please let me know if you need to see any logs or anything else.