Please note that the update process is executed by Joomla! itself, not our code. I believe that your problem is a badly configured / unwriteable tmp directory or missing FTP configuration in your Global Configuration. You can find common troubleshooting instructions for Joomla!'s extensions installer/updater in https://www.akeebabackup.com/documentation/troubleshooter/abinstallation.html
Nicholas K. Dionysopoulos
Lead Developer and Director
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