Slate: IE9-IE11 undefined Symbol

[bkniffler]

Hey,
Like @arekkas already mentioned in https://github.com/ianstormtaylor/slate/issues/146, there seems to be a problem with "Symbol" being undefined on IE9-IE11. It is thrown in https://github.com/ianstormtaylor/slate/blob/40367533358854ccb277d5e06900226e0f188107/src/utils/memoize.js#L58, due to babel transforming it to

for (var _iterator = properties[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
      _loop();
    }

I'm using polyfill.io which polyfills Symbol, but for some reason it still throws the undefined error.

I've not had any other issues with missing features, do you guys have an idea where this could come from?

// Edit
Isn't Symbol an Es6 feature? Shouldn't this be picked up by webpack/browserify?

// Edit2
Obviously, I'll need to use https://cdn.polyfill.io/v2/polyfill.js?features=es6 for this to work.

[Craga89]

Fixed on merge of #729