[BUG] Proxy breaks ES6 Maps and Sets

[rghamilton3]

I think this is related to #367. Attempting to call a function for a map or set stored in state results in

TypeError: Method Set.prototype.entries called on incompatible receiver [object Object]
    at Proxy.entries (<anonymous>)
    at Proxy.func.func (Proxyfier.js:248)

I've confirmed that the same map and set work if they're not in state.

[christianalfoni]

This should be fixed in next release, 4e6f424