Allow the development version (= master branch) of Ruby 3.1

Author: mame

error_highlight.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/ruby/error_highlight"
 
   spec.license       = "MIT"
-  spec.required_ruby_version = Gem::Requirement.new(">= 3.1.0")
+  spec.required_ruby_version = Gem::Requirement.new(">= 3.1.0.dev")
 
   spec.files = Dir.chdir(File.expand_path(__dir__)) do
     `git ls-files -z`.split("\x0").reject { |f| f.match(%r{\A(?:test|spec|features)/}) }