[v3] Queries with equalTo() return null

Hey,

The following code returns `null`, however I do get a correct response using Firebase Web API.
```js
firestack.database.ref('messages').orderByChild('uid').equalTo('wIRBRv9SdtfO7EUdhqL45tLhkzm2').on('value', (snapshot) => {
  console.log(snapshot.val());
});
```

Any ideas? Thanks for all the effort, much appreciation here

Edit: Using iOS