Rakefile in henkei-1.20.0 vs Rakefile in henkei-1.21.0

@@ -1,5 +1,6 @@
 #!/usr/bin/env rake
+# frozen_string_literal: true
 
 require 'bundler/gem_tasks'
 require 'rspec/core/rake_task'
 
 RSpec::Core::RakeTask.new 'spec'