Cannot use bindTo in version 1.0.0-alpha3

According to document we can bind view property to `Observable`

```kotlin
val emailAndPasswordValids = Observables.combineLatest(emailValids, passwordValids) { user, pass -> user and pass }

emailAndPasswordValids.bindTo(signInButton.rx.enabled)
```

But `v.1.0.0-alpha3` the `rx.enabled` is no longer  `MutableProperty`.

Is there any work around to use `bindTo`?