Ubuntu support

Hi there Petr,

We were using your project on our team and it was awesome.
But some of our team members used Ubuntu and they could not benefit from the notifications.

There was @crabhi's [project](https://github.com/crabhi/karma-ubuntu-reporter) that would do notifications for Ubuntu, forked from yours, but it would not allow us to have it running nicely with the Mac.

I [forked](https://github.com/bltavares/karma-notification-reporter) the project to unify both works so we could use them on our team, but I believe that it would be nice to merge it back with your project.

If you like the changes, I would like to propose as well to change the name to `karma-notification-reporter`.
I have reserved the name on npm already and I would pass it to you.

I hope you enjoy the patch.