Nix: Update flake.

Change-Id: I93e0433e124c087a4ca284d35975769a43944a15
diff --git a/flake.lock b/flake.lock
index 520f11f..ef98637 100644
--- a/flake.lock
+++ b/flake.lock
@@ -18,11 +18,11 @@
     },
     "flake-utils": {
       "locked": {
-        "lastModified": 1629284811,
+        "lastModified": 1629481132,
         "narHash": "sha256-JHgasjPR0/J1J3DRm4KxM4zTyAj4IOJY8vIl75v/kPI=",
         "owner": "numtide",
         "repo": "flake-utils",
-        "rev": "c5d161cc0af116a2e17f54316f0bf43f0819785c",
+        "rev": "997f7efcb746a9c140ce1f13c72263189225f482",
         "type": "github"
       },
       "original": {
@@ -33,11 +33,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1629466665,
-        "narHash": "sha256-IZ726OdbYsdGxMa4Cae54jmfbTpgfFJRr5q7Fr7a4RM=",
+        "lastModified": 1629788769,
+        "narHash": "sha256-nKIVCgV9fc0yQL2kRj5vJVhWg8YBq03Mp9XDhrjQlhE=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "63047a07e9c7f376803ff7f971fc951585f0bfae",
+        "rev": "dcc8b48d58ffaab7086f7ee03b3ca0536e5558be",
         "type": "github"
       },
       "original": {
diff --git a/flake.nix b/flake.nix
index 89ee1f4..89dad17 100644
--- a/flake.nix
+++ b/flake.nix
@@ -53,15 +53,8 @@
                 (self.callHackage "optics-core" "0.4" { });
               optics-th = pkgs.haskell.lib.dontCheck
                 (self.callHackage "optics-th" "0.4" { });
-              optics-extra = pkgs.haskell.lib.dontCheck (
-                self.callHackageDirect
-                  {
-                    pkg = "optics-extra";
-                    ver = "0.4";
-                    sha256 = "sha256-oKV8oF0oNHyuActOA7uxBkBzlTgG8LapcKrApa2Pg6U=";
-                  }
-                  { });
-
+              optics-extra = pkgs.haskell.lib.dontCheck
+                (self.callHackage "optics-extra" "0.4" { });
             };
 
             modifier = drv: