Add steep gem

Author: sue445

ruby_header_parser.gemspec

@@ -43,6 +43,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rspec-temp_dir"
   spec.add_development_dependency "rubocop"
   spec.add_development_dependency "rubocop_auto_corrector"
+  spec.add_development_dependency "steep"
   spec.add_development_dependency "yard"
 
   # For more information and examples about making a new gem, check out our