Problem: not testing against latest nixpkgs (also)
Problem: not testing against latest nixpkgs (also)

We should test against the latest nixpkgs to find out any incoming
issues before we bump.

Solution: Add fractalide-nixpkgs-unstable job.

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