Move development dependencies to Gemfile

Author: nobu

Gemfile

@@ -6,3 +6,9 @@ if RUBY_VERSION >= "3.0.0"
   gem "rbs", "~> 3.4"
   gem "rdoc"
 end
+
+group :development do
+  gem "bundler"
+  gem "rake"
+  gem "test-unit"
+end

mutex_m.gemspec

@@ -20,8 +20,4 @@ Gem::Specification.new do |spec|
 
   spec.files = %w[LICENSE.txt README.md lib/mutex_m.rb]
   spec.required_ruby_version = ">= 2.5"
-
-  spec.add_development_dependency "bundler"
-  spec.add_development_dependency "rake"
-  spec.add_development_dependency "test-unit"
 end