How to make the tray flicker when the window is not focused?

[huiruo]

In electron I use like this(js code):

if (!win.isFocused()) { 
            win.showInactive()  //show and not focused
            win.flashFrame(true) //flicker to attract the user's attention 
 }

How do I implement the function in astilectron? Thanks a lot!

[asticode]

As I mentioned in #169, I won't have time to work on this any time soon, therefore if anybody feels like implementing that I'd be happy to review a PR.