How to run crontab for Magento upgrade

I have Magento 2.0.7 and i want to upgrade to 2.1.5 which is the latest version of Magento but I’m having a problem with crontab when i try to upgrade the system and I do Readiness check it gives me a problem :

Example link

I tried this tutorial: http://devdocs.magento.com/guides/v2.0/comp-mgr/upgrader/upgrade-checklist.html

and i used these lines:

* * * * * /usr/bin/php /var/www/magento/bin/magento cron:run | grep -v "Ran jobs by schedule" >> /var/www/magento/var/log/magento.cron.log
* * * * * /usr/bin/php /var/www/magento/update/cron.php >> /var/www/magento/var/log/update.cron.log
* * * * * /usr/bin/php /var/www/magento/bin/magento setup:cron:run >> /var/www/magento/var/log/setup.cron.log```  

but it's not working