Cannot find module 'sass'

[villander]

'use strict';

var sass = require('sass');
const EmberApp = require('ember-cli/lib/broccoli/ember-app');

module.exports = function(defaults) {
  let app = new EmberApp(defaults, {
    // Add options here
    sassOptions: {
      implementation: sass
    }
  });

  // Use `app.import` to add additional libraries to the generated
  // output files.
  //
  // If you need to use different assets in different
  // environments, specify an object as the first parameter. That
  // object's keys should be the environment name and the values
  // should be the asset to use in that environment.
  //
  // If the library that you are including contains AMD or ES6
  // modules that you would like to import into your application
  // please specify an object with the list of modules as keys
  // along with the exports of each module as its value.

  return app.toTree();
};

➜ flexbox-app git:(master) ✗ ember s Could not require 'ember-cli-build.js': Cannot find module 'sass'

Stack Trace and Error Report: /var/folders/1c/5t4__m4j72zfnrchkthtmh8c0000gn/T/error.dump.10b05e33237a0aabe49205f7efb7b06c.log

[jrjohnson]

There is some info here that looks like it will fix this: https://www.npmjs.com/package/ember-cli-sass/v/9.0.0#upgrading-from-a-version-before-v900