Improve update.sh script to fetch latest version automatically

pkgs/applications/editors/jupyter-kernels/iruby/update.sh

@@ -1,6 +1,13 @@
-#!/usr/bin/env sh
+#!/usr/bin/env bash
 
-# First, manually update Gemfile
+set -eu -o pipefail
+
+cd "$(dirname "$0")"
+
+# Update Gemfile with the latest iruby version
+echo "source 'https://rubygems.org'" > Gemfile
+echo -n "gem 'iruby', " >> Gemfile
+nix shell .#curl -c curl https://rubygems.org/api/v1/gems/iruby.json | nix shell .#jq -c jq .version >> Gemfile
 
 # Regenerate Gemfile.lock
 nix shell .#bundler -c bundle lock