Add support for a default to Shell::Basic#ask

```rb
> shell.ask "Pick a race", default: "Terran"
Pick a race ("Terran")
= "Terran"
> shell.ask "Pick a race", default: "Terran"
Pick a race ("Terran") Zerg
= "Zerg"
> shell.ask "Pick a race", default: "Terran", limited_to: %w[Terran Zerg Protoss]
Pick a race ["Terran", "Zerg", "Protoss"] ("Terran") Human
Your response must be one of: ["Terran", "Zerg", "Protoss"]. Please try again.
Pick a race ["Terran", "Zerg", "Protoss"] ("Terran")
= "Terran"
```