oset being strict

Hello,

I'm trying to use oops to interop with [Automerge](https://github.com/automerge/automerge).

This snippet fails to make an update:

```clojure
(oset+ doc "todos" (str idx) "done" true)
```

The browser complaints that: `data property descriptor has writable=false`

But if I try something a bit different:

```clojure
(gobj/set (oget+ doc "todos" (str idx)) "done" done)
```

This works just fine, the google impl is a single `obj[key] = value`. I wonder if there is a way to make `oops` work directly without having to fall back into Closure helpers.