-0 is not normalized

In JavaScript `Map` and `Set` do not distinguish `0` and `-0` as different keys, instead `-0` is normalized to `0`.

This leads to the following 'bug':

```js
const { tuple } = require("immutable-tuple");

if (Math.random() > 0.5) {
tuple(Object, -0); // sometimes create this first
} else {
tuple(Object, 0); // other times create this first
}

function isNegativeZero(n) {
return Object.is(n, -0);
}

console.log(isNegativeZero(tuple(Object, -0)[1])); // sometimes 'true', sometimes 'false'
```