Due to the restricted shell when using cron through cPanel, I had to change the cron command to:
PATH=/usr/bin:/bin:/usr/local/bin && cd /usr/local/bin && ./wp-update /home/xxxxx/public_html/
in order to get it to run.
Otherwise I just got "/usr/local/bin/wp-update: line 21: wp: command not found"
Hope this helps someone.

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