The way RunKit notebooks work is that they are locked to the original version of the package they use. That way, if you return to a notebook a day later, running it wouldn't accidentally get you a different package. In order to "reset" it and get the latest package, you can delete the reference to it, run, and then add it back in. This isn't ideal we know, but we are working on better UI to make it more reasonable.
Sorry for the confusion!