ES6 errors when bundling (jspm) a React/jsx app

I'm trying to setup a project using jspm. I've follows this great tutorial and it works pretty good, except when I try to bundle

$> jspm bundle-sfx app.jsx! app.js --skip-source-maps --minify
Building the single-file sfx bundle for app.jsx!...

err MultipleErrors: cartItem.jsx:5:22: Unexpected token =
      cartItem.jsx:6:21: Unexpected token .
      cartItem.jsx:6:22: Unexpected token PropTypes
      cartItem.jsx:6:31: Unexpected token .
      cartItem.jsx:7:14: Semi-colon expected
      cartItem.jsx:7:14: Unexpected token :

(app.jsx, cartItem.jsx, and github project)

I get the impression that the bundle tool doesn't understand es6, right?

Any suggestions what I'm doing wrong here?

Also, what does the ! mean following the filename app.jsx?

I have test the following steps and it works fine:

By the way, my jspm version is 0.16.12 by jspm -v.

$ git clone https://github.com/egor-smirnov/egorsmirnov.me-examples.git
$ cd egorsmirnov.me-examples/react-and-es6-part-5/
$ jspm init
$ jspm install
$ jspm bundle-sfx app.jsx! app.js --skip-source-maps --minify