nomad: restructure to use multiple files

as per request in PR comments, used generic.nix with version files

pkgs/applications/networking/cluster/nomad/0.11.nix

@@ -0,0 +1,6 @@
+{ callPackage }:
+
+callPackage ./generic.nix {
+  version = "0.11.4";
+  sha256 = "1sykp9sji6f564s7bz0cvnr9w5x92n0l1r1djf1bl7jvv2mi1mcb";
+}

pkgs/applications/networking/cluster/nomad/0.12.nix

@@ -0,0 +1,6 @@
+{ callPackage }:
+
+callPackage ./generic.nix {
+  version = "0.12.2";
+  sha256 = "1gc286ag6plk5kxw7jzr32cp3n5rwydj1z7rds1rfd0fyq7an404";
+}

pkgs/applications/networking/cluster/nomad/generic.nix

@@ -1,19 +1,4 @@
-{ stdenv, buildGoPackage, fetchFromGitHub, majorVersion ? "0.11" }:
-
-let
-  versionMap = {
-    "0.11" = {
-      version = "0.11.4";
-      sha256 = "1sykp9sji6f564s7bz0cvnr9w5x92n0l1r1djf1bl7jvv2mi1mcb";
-    };
-    "0.12" = {
-      version = "0.12.2";
-      sha256 = "1gc286ag6plk5kxw7jzr32cp3n5rwydj1z7rds1rfd0fyq7an404";
-    };
-  };
-in
-
-with versionMap.${majorVersion};
+{ stdenv, buildGoPackage, fetchFromGitHub, version, sha256 }:
 
 buildGoPackage rec {
   pname = "nomad";

pkgs/top-level/all-packages.nix

@@ -5609,8 +5609,8 @@ in
   noip = callPackage ../tools/networking/noip { };
 
   nomad = nomad_0_11;
-  nomad_0_11 = callPackage ../applications/networking/cluster/nomad { majorVersion = "0.11"; };
-  nomad_0_12 = callPackage ../applications/networking/cluster/nomad { majorVersion = "0.12"; };
+  nomad_0_11 = callPackage ../applications/networking/cluster/nomad/0.11.nix { };
+  nomad_0_12 = callPackage ../applications/networking/cluster/nomad/0.12.nix { };
 
   notable = callPackage ../applications/misc/notable { };