Dates don't work in selectors

[mattcolman]

Oh hi,

First time issue creator, long time fan of react-sweet-state.

I've noticed that if you return a Date from a selector then React components don't update.
After some digging I've found that when "update" runs it does a "shallowEqual" against previous and current values. Two different Dates are returning true with the custom shallowEqual function and therefore components never update. See screenshot for a test I wrote.

Workaround for now is to wrap the date in an object like selector: state => ({ date: state.myDate })

Perhaps we can just add another "if statement" for instanceof Date to shallowEqual?

Thanks!!

[fkrafi]

@albertogasparin , i have tried to fixed the bug, can you please verify, here is the PR #147

[albertogasparin]

Fixed in #147