onebox.gemspec in onebox-1.8.22 vs onebox.gemspec in onebox-1.8.23

- old
+ new

@@ -1,5 +1,7 @@
+# frozen-string-literal: true
+
 # coding: utf-8
 lib = File.expand_path('../lib', __FILE__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'onebox/version'
 
@@ -38,6 +40,8 @@
   spec.add_development_dependency 'guard-rspec', '~> 4.2.8'
   spec.add_development_dependency 'sinatra', '~> 1.4'
   spec.add_development_dependency 'sinatra-contrib', '~> 1.4'
   spec.add_development_dependency 'haml', '~> 4.0'
   spec.add_development_dependency 'listen', '~> 2.10.0'
+
+  spec.required_ruby_version = '>=2.2.0'
 end