heroku deploy error build script 'better-npm-run build'

seems adding a version fix into `package.json` does not really work, `"engines": {
"node": "6.9.x"
}`

note: Error above is when without a `engines` set, but even when I did push the new code above up, and the error still persist. Thought?

and this error when I ran with 6.9.x