Can't build Ember.js app embedded in Rails app on Heroku

Trying to build Ember.js app embedded in Rails app on Heroku, but get this error:

Could not require 'ember-cli-build.js': Cannot find module 'ember-cli/lib/broccoli/ember-app'

Rail's package.json:

{
  "name": "foo",
  "license": "MIT",
  "engines": {
    "node": "9.5.0",
    "yarn": "1.22.4"
  },
  "scripts": {
    "build": "yarn global add ember-cli@2.9.0 --ignore-engines && yarn --cwd ember install --ignore-engines && yarn --cwd ember build"
  }
}

Ember's package.json:

{
  "name": "foo",
  "version": "0.0.0",
  "description": "foo",
  "private": true,
  "directories": {
    "doc": "doc",
    "test": "tests"
  },
  "scripts": {
    "build": "ember build",
    "start": "ember server",
    "test": "ember test"
  },
  ...
}

This Ember.js app as stand-alone, i.e. not being embedded in Rails app, is deployed on Heroku without errors.