Game cannot be played with different Game Ids because it always loads the first played game

You have to provide an override for ToString on the GameId single case discriminated union, because otherwise the streamId is always formatted like `Game-FsUno.Domain.Game+GameId`.

``` fsharp
type GameId = GameId of int with
    override self.ToString() =
        let (GameId id) = self in id.ToString()
```
