Try...
wget -q -0 /dev/null --header='X-API-Key: <API-KEY-HERE>' http://myhost.com/support/api/tasks/cron
Follow the steps below when using rcron.php
1. Upload rcron.php to a directory or your choice - I recommend creating unique/ramdom name somewhere on the web server path or simply rename rcron.php to a name of your choice.
2. Edit rcron.php to add API key and change the url.
The url should be http://myhost.com/support/api/tasks/cron(http://myhost.com/support/api/tasks/cron).
Note lack of .php extension and tasks not task (as of RC6)
3. In your host panel - create a cron entry to point to rcron.php (based on where you put it in step #1) or use crontab entry below.
wget -q -0 /dev/null http://myhost.com/support/api/tasks/cron