Node engine 8.x or 10.x in package.json

See the documentation which includes examples.

Provide a space separated list of engines with greater/less than symbols.

{ 
  "engines" : { 
    "node" : ">=8.0.0 <11.0.0" 
  }
}

You just need the double pipe || instead of a single.

"engines": {
  "node": "^8 || ^10"
}

Would match either v8.x.x or v10.x.x but not v9.

You can read more about it here, or https://github.com/npm/node-semver#versions