prometheus-node-exported: fix output cycle on darwin

pkgs/servers/monitoring/prometheus/node-exporter.nix

@@ -14,6 +14,10 @@ buildGoPackage rec {
     sha256 = "0rm43jjqv7crfahl973swi4warqmqnmv740cg800yvzvnlp37kl4";
   };
 
+  preFixup = stdenv.lib.optionalString stdenv.isDarwin ''
+    install_name_tool -delete_rpath $out/lib $bin/bin/node_exporter
+  '';
+
   # FIXME: megacli test fails
   doCheck = false;