Updated so it uses Joomla updater.

Please uninstall the old version first and then install this new one.
The plugin is now setup with a Joomla Extension Update server.
Now you can easily install updates by using the Joomla updater. There is
no need anymore to manually update the Mobile_Detect.php library. This
will now be updated to the latest version through the Joomla updater.
Thanks Peter Martin @pe7er for this tip!