Stacker: tool to bump snapshots in `stack*.yaml` files

Thanks, @janus, for the pointer. I installed stack-lint-extra-deps and it seems very useful. Also, it seems to be implemented in a better way than my tool, as it queries stackage.org for the list of resolvers (fast), whereas my tool clones the stackage-snapshots repo and constructs the information from there (slow).

However, stack-lint-extra-deps does not fit my purpose because it has only two snapshot categories, lts or nightly, so I will bump any lts constraint to the absolutely latest lts, whereas I want the latest lts for the respective GHC major version.

So this is not good if you want to maintain build with older GHCs.

Also, it appears not to be released on Hackage so it might just disappear at any time.