Mutations not firing when clicking "Pull Requests" tab

[stl-gilesbartonowen]

I noticed that although the "comments" event fires on most PR events, now when you hit "Pull Requests" it doesn't fire. I've fixed this by adding ".new-discussion-timeline" to the comments event target. I believe this is how this event is meant to function and I think this is potentially a change in github's code.

Thanks for an awesome piece of work!