Object.setPrototypeOf sham

As discussed already in [this thread](https://github.com/paulmillr/es6-shim/pull/223#issuecomment-51696022) here a cross browser/platform `Object.setPrototypeOf` that works reliably **requiring** reassignment of the same object, meaning external, non own objects, might not be upgraded if the engine was not compatible.

As sham, this does not require `es6-shim` as is.
I don't think so, I've just used `npm install` once I've forked the repo so the version is the one specified already. If it's specified as `>=` then it's repo choice, not mine to define the minimum.

I think either you guys ignore `node_modules` or simply `npm update` or `npm install` again locally too