Update screenshot on AMO and Chrome Web Store

[fregante]

https://chrome.google.com/webstore/developer/dashboard/

https://github.com/tanmayrajani/notifications-preview-github/blob/master/media/screenshot.png

[tanmayrajani]

Done. Updated. Thanks for reminding :)

[tanmayrajani]

I see the screenshot on AMO is old one as well. Let's update that too. @bfred-it can you please do that?

[fregante]

Thanks for the reminder, :D changing now.

Are you on AMO? What's your address? I can add you as a collab

[tanmayrajani]

Sure, my username is "tanmayrajani" on AMO.

[fregante]

Email needed:

[fregante]

Done, thanks!