Start with bundlerEnv for the convert script

default.nix

@@ -0,0 +1,10 @@
+{ bundlerEnv, ruby }:
+
+bundlerEnv {
+  inherit ruby;
+
+  name = "render-test";
+  gemfile = ./Gemfile;
+  lockfile = ./Gemfile.lock;
+  gemset = ./gemset.nix;
+}