Update dependencies to allow route guard code to work

[ghostal]

Hi @Gregg! First off, thanks a lot for the course. I'm enjoying learning from it, and especially enjoying the outtakes :smile:

I came across a problem with the route guard code, whereby Vue would complain that next() wasn't being run, meaning it considered the route guard to be invalid. Eventually I found the helpful comments by and @platoputhur @Bruce9000 in issue #2.

That got me back on track, and I thought I'd open a PR so the code can be easily updated.

All I've done here is run npm update on the end of the L9-start branch and commit the updated package-lock.json.

As far as I can gather, the key change the solves the problem is that the vue-router package moves from 4.0.0-beta.9 to 4.0.12.