Support for Vue 3

When attempting to put this in a Vue 3 project, I get the following during `npm install`:

```
npm ERR! Could not resolve dependency:
npm ERR! peer vue@"2.x" from @politico/vue-accessible-selects@0.13.1
```

I'm not sure if there is more to it than just updating the package.json file - I will experiment with that in a couple days.
