prereq install fails on latest stable node version

[sneak]

I'm a developer/entrepreneur. I use steemit all the time and want to add a feature to condenser. I make a blog post and it gets widespread support. I make an issue in the issue tracker proposing it and TPTB say it'd get merged if I wrote it.

I sit down to my brand new freshly installed Macintosh with High Sierra and install Xcode and homebrew. I brew install node and npm install -g yarn to bring up a dev environment. I clone condenser and check out master with the plan to run the tests to verify my dev environment baseline is set up correctly. I get an error because it can't install on the latest stable version of node that homebrew installs.

✔ ~/tmp/condenser [master|…1] 
23:15 $ yarn install
yarn install v1.3.2
[1/5] 🔍  Validating package.json...
[2/5] 🔍  Resolving packages...
[3/5] 🚚  Fetching packages...
error @steemit/rpc-auth@1.1.0: The engine "node" is incompatible with this module. Expected version "^8".
error Found incompatible module
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
✘-1 ~/tmp/condenser [master|…1] 
23:18 $ node -v
v9.4.0
✔ ~/tmp/condenser [master|…1] 
23:18 $ 

I know node 8 is LTS, but that doesn't actually matter at all if you read that user story.

[sneak]

I believe this just requires an rpc-auth bamp (plus associated runtime-major-version-number-change QA and testing) because steemit/rpc-auth#16 is already done and merged.