Gemfile in in_threads-1.5.1 vs Gemfile in in_threads-1.5.2

@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 gemspec
 
 gem 'rspec-retry', '< 0.6.1' if RUBY_VERSION < '1.9'