keep hack for ancient rubys

Author: rarruda

unleash-client.gemspec

@@ -40,9 +40,11 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "simplecov", "~> 0.21.2"
   spec.add_development_dependency "simplecov-lcov", "~> 0.8.0"
 
-  # NOTE: only require rbs/steep in MRI ruby versions. Ignore jruby.
-  unless RUBY_ENGINE == 'jruby'
+  # NOTE: only require rbs/steep in supported ruby versions. In EOL ruby/jruby, just ignore.
+  # rubocop:disable Gemspec/RubyVersionGlobalsUsage
+  if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('3.1')
     spec.add_development_dependency "rbs", "~> 3.8.1"
     spec.add_development_dependency "steep", "~> 1.9.3"
   end
+  # rubocop:enable Gemspec/RubyVersionGlobalsUsage
 end