Spectral 5.0.0 on macOS

Question , using spectral on macOS

I installed the binary for spectral on MacOS Mojave.
spectral --version
npm --version

I was able to successfully run Spectral against a local ruleset file,
spectral lint swagger.json --ruleset=/Users/adrian/Downloads/spectral2.yml

OpenAPI 2.0 (Swagger) detected


182:12 warning model-definitions-examples Model property examples SHOULD be present and non-empty string.

but when I add the line:
extends: spectral:oas2

as the first line to my local ruleset I get the error below

spectral lint swagger.json --ruleset=/Users/adrian/Downloads/spectral2.yml
Could not parse https://unpkg.com/spectral:oas2: Forbidden

Any pointers on what I am doing wrong greatly appreciated.