Iterable WeakMap implementation in README is incorrect?

[benjamingr]

See discussion here: nodejs/node#35915 (comment)

The set implementation always creates a new WeakRef which means that seting the same thing twice sets two keys since:

var m = new Map();
var o = {};
var r1 = new WeakRef(o);
var r2 = new WeakRef(o);
m.set(r1, "foo");
console.log(m.get(r1)); // foo 
console.log(m.get(r2)); // undefined

cc @bcoe