Update the minimum requirement of Ruby version

Author: hsbt

io-console.gemspec

@@ -7,7 +7,7 @@ Gem::Specification.new do |s|
   s.summary = "Console interface"
   s.email = "[email protected]"
   s.description = "add console capabilities to IO instances."
-  s.required_ruby_version = ">= 2.2.0"
+  s.required_ruby_version = ">= 2.4.0"
   s.homepage = "https://github.com/ruby/io-console"
   s.metadata["source_code_url"] = s.homepage
   s.authors = ["Nobu Nakada"]