[default.nix] Update pinned nixpkgs.
[default.nix] Update pinned nixpkgs.

ejgallego/coq,Zimmi48/coq,silene/coq,gares/coq,ppedrot/coq,gares/coq,maximedenes/coq,JasonGross/coq,JasonGross/coq,coq/coq,ppedrot/coq,Matafou/coq,SkySkimmer/coq,ejgallego/coq,maximedenes/coq,coq/coq,ejgallego/coq,SkySkimmer/coq,Zimmi48/coq,Zimmi48/coq,SkySkimmer/coq,ppedrot/coq,Zimmi48/coq,maximedenes/coq,maximedenes/coq,coq/coq,maximedenes/coq,Matafou/coq,gares/coq,ppedrot/coq,silene/coq,silene/coq,gares/coq,gares/coq,ejgallego/coq,JasonGross/coq,coq/coq,SkySkimmer/coq,JasonGross/coq,Matafou/coq,ppedrot/coq