Hi
Yes the documentation is very out of date for the latest SDK, unfortunately 
You can make this work though - before you create the visual, you'll need to make sure the SDK is "downgraded" to work with the version in the tutorial. In this section, modify step 2 as from:
npm i -g powerbi-visuals-tools
to:
npm i -g powerbi-visuals-tools@2.5
You should then be able to continue the tutorial as normal.
Note that the latest SDK changes a lot of how visuals are built (which is the error you're probably seeing - there have been quite a few posts on this subject recently... hopefully MS will update the doc soon...), but the code concepts are pretty much the same, even though you're using an older version.
Good luck!
Daniel