Problem: Our pinned nixpkgs is old
Problem: Our pinned nixpkgs is old

Sooner or later our dependencies will fall out of the hydra cache.

(for racket2nix this already happened, see next commit)

Solution: Bump nixpkgs.

fractalide/fractalide,sjmackenzie/fractalide,fractalide/fractalide,sjmackenzie/fractalide,sjmackenzie/fractalide,dmichiels/fractalide,fractalide/fractalide,dmichiels/fractalide,dmichiels/fractalide