[docs] [examples] useImmer To-do list example is using wrong object property for `checked`

[Navid Mafi]

🐛 Bug Report

sorry for not following the issue template since this is a very minor issue

Currently useImmer example which is here uses todo.finished for checkboxes checked value which is wrong and should be changed to todo.done

https://codesandbox.io/s/use-immer-bvd5v?file=/src/index.js

should be changed to