Passive event listeners are an emerging web standard, new feature shipped in Chrome 51 that provide a major potential boost to scroll performance. This warning is being thrown in Chrome 51 browsers.
Link for fix:
I came here looking for passive support too. Get that updated soon.
It's been a while since the author himself has updated the repo - I reached out to him via Twitter as well in hopes to breathe some new life into this project. In the meantime - is this something you could work on and submit a pull request?