Transforms not being applied on .require()'d file

I originally posted this issue over at [babelify](https://github.com/babel/babelify/issues/147), but I have the feeling it's actually more general.

I've created a repo to showcase this issue, it can be found at https://github.com/chielkunkels/browserify-issue. Deleting line 16 in the gulpfile (https://github.com/chielkunkels/browserify-issue/blob/master/gulpfile.js#L16) get rid of the error during bundling. While it can easily be omitted here, that's not the case for the code I actually need it for.

Hope there's some kind of fix for this. Cheers!