Does not shake off other modules when importing with default

[z-vr]

This plugin works great but unfortunately it does not allow to import default exports only.

Steps to reproduce:

1. Checkout https://github.com/Sobesednik/bs-sh on github
2. git clone https://github.com/Sobesednik/bs-sh.git
3. cd bs-sh
4. npm i
5. npm t

[goto-bus-stop]

This is most likely because default imports get wrapped in a _interopDefault function call by Babel. common-shake does not know what this function does (it could do anything) so it marks all properties of the entire require() call as "used" just to be safe. common-shake works best with untranspiled CommonJS modules. ES modules will likely get better support in browserify itself after Node settles on an implementation.