TypeError: can't redefine non-configurable property 'define'

I get this error when trying to use this package:

```
Timestamp: 12-04-23 10:47:26 PM
Error: An exception occurred.
Traceback (most recent call last):
File "resource://jid0-hc7vb1gcmvr7ibb5b5adujtjb3u-at-jetpack/io/lib/@modules/raw.github.com/Gozala/events/v0.5.0/events.js", line 5, in
(typeof define !== "function" ? function($){ $(require, exports, module); } : define)(function(require, exports, module, undefined) {
File "resource://jid0-hc7vb1gcmvr7ibb5b5adujtjb3u-at-jetpack/api-utils/lib/globals!.js", line 75, in getter
value: define.bind(this)
TypeError: can't redefine non-configurable property 'define'
```

What I've done is cloned jetpack-io in the packages sub-directory of my add-on, then run git submodule init in the clone. In my code, all I have is this:

```
const fs = require("io/fs");
```

User error?