Changes to use node-notifier directly.

I saw you were using the `gulp-notify` on an "empty" stream from gulp. I don't think there is much need to have the overhead of creating a stream with the base folder in order to do the notification. Instead, you can use [node-notifier](https://github.com/mikaelbr/node-notifier) directly (which `gulp-notify` uses internally).

The one drawback of doing it this way, is that it won't have the gulp-notify defaults with a Gulp logo as icon.