Observable is not defined error while trying localForage.newObservable({})

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I'm working on Angular@16.2.1 with localforage@1.10.0 and localforage-observable@^2.1.1

Just following the same steps as in documentation, but getting error in **localforage.newObservable()**. Tried with different versions of localforage-observable also, but nothing works
```
import localForage from "localforage";
// OR based on your configuration:
// import * as localForage from "localforage";

import { extendPrototype } from "localforage-observable";

var localforage = extendPrototype(localForage);
localforage.ready().then(() => {
// TypeScript will find `newObservable()` after the casting that `extendPrototype()` does
var observable = localforage.newObservable();
});
```

Following error while running application:
```
Unhandled Promise rejection: Observable is not defined ; Zone: ; Task: Promise.then ; Value: ReferenceError: Observable is not defined
at newObservable.factory (localforage-observable.js:444:9)
at LocalForage.newObservable (localforage-observable.js:431:40)
```

Start with the documented `extendPrototype()` and `newObservable()` example, then inspect the `newObservable.factory` and `LocalForage.newObservable` locations shown in `localforage-observable.js`. Reproduce the Angular 16.2.1 setup with localForage 1.10.0 and localforage-observable 2.1.1; done means creating the observable no longer raises `ReferenceError: Observable is not defined`.

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