switched args in storage.forEach documentation

From the documentation, "To enumerate the stored key/value pairs" should be :

```
storage.forEach((key, value, index) => {
});
```
but when I use it, the valid syntaxe is :
```
storage.forEach((value, key, index) => {
});
```

Start with the documentation section titled "To enumerate the stored key/value pairs" and verify the callback argument order against the storage.forEach API usage shown in the issue. Done means the example documents value, key, and index in the valid order.

Vom Indexierungsmodell aus dem Issue-Text verfasst.