`stack.yaml` in error (3.12 in stead of 13.12)

[andrewufrank]

The stack.yaml file is in error. it says lts-3.12, but should probably say 13.12. the extra-deps are also old. it should say: resolver: lts-13.12

packages:

• '.' extra-deps:

flags: {}

sorry for not sending a PR - issues with githup protection on my side.

[mpickering]

I think 3.12 is probably right as that fits in with around when I made the project in 2015.

I don't use stack though and as you can probably see, I only do the bare minimum level of maintenance on the repo so I will remove the stack.yaml script.