Commit 72557f2

@@ -5,7 +5,7 @@ AllCops:
     - 'test/**/*'
     - 'tmp/**/*'
     - 'vendor/**/*'
-  TargetRubyVersion: 2.6
+  TargetRubyVersion: 2.4
 
 Layout/AlignParameters:
   EnforcedStyle: with_fixed_indentation

@@ -1,4 +1,5 @@
 Version 0.2.6
+
 # Changelog
 All notable changes to this project will be documented in this file.
 
@@ -6,6 +7,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Changed
+- specify ruby 2.4 and minimum required.
 
 ## [0.2.6] - 2019-04-30
 ### Added

@@ -21,6 +21,7 @@ Gem::Specification.new do |spec|
   spec.bindir        = 'exe'
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
+  spec.required_ruby_version = '~> 2.4'
 
   spec.add_development_dependency 'minitest', '~> 5.0'
   spec.add_development_dependency 'rake', '~> 10.0'