Broken build when requiring moment-timezone and moment

`factor-bundle` creates broken bundles when required modules have linked dependencies. This happens for example when installing `moment-timezone` and afterwards `moment`. So `moment` exists two times in the `node_modules` folder, once for `moment-timezone` and once in `moment`. This seems to break browserify. When installing the modules the other way around the bundle does not break (this time there is only one `moment`).

I don't know if this is more of a problem with the way npm install modules when they have duplicate dependencies or if this is a problem with factor bundle.

I set up a test case over at: https://github.com/davidlanger/factor-bundle-moment-timezone