imap-backup.gemspec in imap-backup-4.0.2 vs imap-backup.gemspec in imap-backup-4.0.3

@@ -22,9 +22,10 @@
   gem.require_paths = ["lib"]
   gem.required_ruby_version = ">= 2.5"
 
   gem.add_runtime_dependency "highline"
   gem.add_runtime_dependency "mail"
+  gem.add_runtime_dependency "os"
   gem.add_runtime_dependency "rake"
   gem.add_runtime_dependency "thor", "~> 1.1"
 
   gem.add_development_dependency "codeclimate-test-reporter", "~> 0.4.8"
   if RUBY_ENGINE == "jruby"