Commit an update to Gemfile.lock when bumping the version.

In ElasticGraph v0.19.0.0 and before, we did not keep the `Gemfile.lock`
under source control, and our release process didn't need to update it
and commit it as part of bumping the version. Now that we keep it under
source control, we need to update it and commit it.

config/release/Rakefile

@@ -10,6 +10,7 @@
 # That's why we get the project root from git instead of using `__dir__`.
 project_root = `git rev-parse --show-toplevel`.strip
 
+require "bundler"
 require "gem/release"
 require "#{project_root}/elasticgraph-support/lib/elastic_graph/version"
 require "#{project_root}/script/list_eg_gems"
@@ -19,6 +20,13 @@ task :bump_version, [:version] do |_, args|
   version = args.fetch(:version)
   ::Dir.chdir(project_root) do
     sh "bundle exec gem bump elasticgraph-support --file #{project_root}/elasticgraph-support/lib/elastic_graph/version.rb -v #{version} -m 'Release v#{version}.'"
+
+    # We also want to commit an update to `Gemfile.lock` as part of the version bump.
+    ::Bundler.with_unbundled_env do
+      sh "bundle install"
+      sh "git add Gemfile.lock"
+      sh "git commit --amend --no-edit"
+    end
   end
 end