I did a saveYesterday.php on your site and forced a collection just to check that the script was running correctly (if invoked). It ran fine and saved today's values at that time to yesterday's values.
So the problem seems to be with trying to run the script via cron. Do you have an email address in cPanel to receive the errors if a cron job fails.. if not, please add it.
On my GoDaddy cPanel site, /usr/bin/php is PHP 7.2 so try:
cd $HOME/public_html;/usr/bin/php -q saveYesterday.php >> cache/LOG_saveYesterday.php.txt
as the command.. if it fails, then, we'll have to use a cron batch file instead (and that's a bit trickier to make work as the batch files have to only have \n (new-line) characters, and \r\n (carriage-return,new-line) like windows uses will blow up a batch job).