Nested collections aren't supported

[BlackBaroness]

Hi!

Seems like Configurate can't handle nested collections, like:

val townTypePrices: Map<Enum, Map<Material, Int>> = mapOf(
        Enum to mapOf(Material.EMERALD to 3, Material.STONE to 100),
        Enum to mapOf(Material.EMERALD to 3, Material.STONE to 100),
        Enum to mapOf(Material.EMERALD to 3, Material.STONE to 100),
    ),

I see the same issue with lists inside lists, etc.
Always had to make an object what will store other collections, and store a list of these objects, but that's not good

When I save it, it always just prints something like town-type-prices: {}