Use "showTemporary" instead of explicitly hiding the notification

"OC.Notification.hide" expects the notification to be hidden to be
passed as an argument. As it was being used to show a temporary
notification the combination of "OC.Notification.show" and
"OC.Notification.hide" was replaced by a single call to
"OC.Notification.showTemporary".

The timeout could have been specified in the options of the call, but it
was left to the default value (7 seconds) for consistency with other
notifications.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>