Read spago.lock as YAML is broken since 0.93.0

[amuricys]

https://github.com/thomashoneyman/purescript-overlay/blob/main/nix/build-spago-lock.nix#L20

This line tries fromYAML, and the spago rewrite stopped emitting .lock files as yaml in favor of .json.

[thomashoneyman]

I should really just take that out of the library altogether, as a better alternative has come out:
https://github.com/jeslie0/mkSpagoDerivation

[thomashoneyman]

This is closed by #127 with the removal of the fromYAML function