flake.nix: add hydraJobs

flake.nix

@@ -5,7 +5,7 @@
     let
       systems = [ "x86_64-linux" "i686-linux" "aarch64-linux" ];
       forSystems = nixpkgs.lib.genAttrs systems;
-    in {
+    in rec {
       packages = forSystems (system:
         import ./default.nix {
           pkgs = nixpkgs.legacyPackages.${system};
@@ -16,6 +16,9 @@
         self.packages.${system}.ticker-serve
       );
 
+      hydraJobs =
+        packages.${builtins.head systems};
+
       devShell = import ./shell.nix {
         pkgs = nixpkgs.legacyPackages.x86_64-linux;
       };