ES6 transpilation is only provided in the dev module loader build, error with es6-module-loader

Why would I get this error with the es6-module-loader:

ES6 transpilation is only provided in the dev module loader build.

here is the code that I am trying to use this with:

System.transpiler = 'babel';
System.import('app/main.js').then(function (module) {
  new module.Main();
});

main.js:

import foo from './foo'

export class Main {
  constructor() {

  }
}

package.json:

devDependencies": {
    "babel-core": "^5.8.22",
    "es6-module-loader": "^0.17.6",
    "object.observe": "^0.2.4",
    "qunitjs": "^1.18.0"
  }

Solution