Allow to specify a custom moduleName

I'm working on a Meteor smart package that compiles Javascript files with Traceur. Because of a limitation of Meteor, the files must end with something else then .js. I use .next.js. Currently '.next' will be part of the moduleName. But I don't want this. With this simple change I can specify the correct moduleName by passing `{moduleName: 'myModuleName'}` for example.

I signed the CLA with Jonas Aschenbrenner (jonas.aschenbrenner@gmail.com). I think I did it already in the past, but I have done it again.