Bump nixpkgs

default.nix

@@ -8,11 +8,12 @@
 #       nix build -f --arg ghc "(import build.nix {ghc-path=$GHC_TREE;})"
 #
 let
-  rev = "e0818a15305561ea1ebe36203d914465fd71453d";
+  # To update nixpkgs bump rev and baseNixpkgs's sha256.
+  rev = "2f746bc1fcdc24b103bda3a27ed82c23200cc077";
   baseNixpkgs =
     fetchTarball {
       url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
-      sha256 = "017j741anrl66nndfmblp6xc1lz7783dh8lf19srmxnk5xk4wn7l";
+      sha256 = "142yl6xakkwmyy8x32h94fci4x09l0yqppq5hwj19a3nmd0zmsjx";
     };
 in