Filename typo: `yaml != json`

[zmrocze]

Hi,
there's a typo, isnt there?
Should be topology.json.

iohk-nix/cardano-lib/default.nix

Line 47 in b426fb9

builtins.toFile "topology.yaml" (builtins.toJSON topology);

[johnalotoski]

Closed by #594, thanks!