`:wq` with `async_write = true` writes but does not quit

Hello!

I just tested the `master` branch with `async_write = true`. Pretty much everything seems to be working, but when using `wq`, the notebook is written but it seems that the async write makes nvim "forget" the quit command.

I know this functionality is for testing currently, but I wanted to open an issue to track this just in case.

Thanks!