Flagrant System Error when importing enzyme with react-dom

Hi, thanks for the awesome tools!

I'm trying to get a sketch running at esnextbin, and am getting a bundling error when I try to import enzyme. I understand that this is likely an issue with enzyme, and I'll go an have a look in their issues, too...

The issue is visible in the following gist if you un-comment the `import {shallow} from 'enzyme';` and the last `it()` test then click 'Execute':

- https://esnextb.in/?gist=8032ddde1be3e4d292b1e7cff6a97891
- https://gist.github.com/ptim/8032ddde1be3e4d292b1e7cff6a97891

Fingers crossed, TIA, ptim

The console then produces:

```
---FLAGRANT SYSTEM ERROR---

--- error #0: ---

(logs uuid: 0ee0b440-c1fe-11e6-95c3-57598f133f70 )

Error: "browserify exited with code 1"

code: 1
stderr: Error: Cannot find module 'react-dom' from '/tmp/enzyme1161114-29462-195j7a7/node_modules/enzyme/build'
at /home/admin/browserify-cdn/node_modules/browserify/node_modules/browser-resolve/node_modules/resolve/lib/async.js:46:17
at process (/home/admin/browserify-cdn/node_modules/browserify/node_modules/browser-resolve/node_modules/resolve/lib/async.js:173:43)
at ondir (/home/admin/browserify-cdn/node_modules/browserify/node_modules/browser-resolve/node_modules/resolve/lib/async.js:188:17)
at load (/home/admin/browserify-cdn/node_modules/browserify/node_modules/browser-resolve/node_modules/resolve/lib/async.js:69:43)
at onex (/home/admin/browserify-cdn/node_modules/browserify/node_modules/browser-resolve/node_modules/resolve/lib/async.js:92:31)
at /home/admin/browserify-cdn/node_modules/browserify/node_modules/browser-resolve/node_modules/resolve/lib/async.js:22:47
at FSReqWrap.oncomplete (fs.js:82:15)

dirPath: /tmp/enzyme1161114-29462-195j7a7

------

This is probably an issue with the package, and not browserify-cdn itself.
If you feel differently, feel free to file a bug report at:

https://github.com/jfhbrook/browserify-cdn/issues

Include the ENTIRETY of the contents of this message, and the maintainer(s)
can try to help you out.

Have a nice day!
```

Reproduce the failure from the linked esnextbin sketch or GitHub gist with the enzyme import and final test enabled. Start by tracing the reported browserify module-resolution error for react-dom from enzyme/build; done means the example bundles and executes without this error.

Written by the indexing model from the issue text.