Quick apology for confusing the terms "push notification" and "desktop notification". I forgot "push" usually refers to sites that use service workers to send notifications to the desktop regardless of whether the browser window is open. This library requires the window remain open for the notification to be shown.
I just tested on Chrome 50.0.2661.102 (64-bit) on OSX 10.11.4 and it seems to work. What OS are you running? Did it ask you permission to show notifications? Are there any errors in the developer console?
I think I ran into the issue before as well.. however, I think that's an issue with how Chrome handles its notifications. I don't think there's anything in the library that could cause this behavior. A known issue is that the library is currently broken in Safari. I will investigate why when I have some free time.