Technical/Update default gemspec (#74)

Author: bestwebua

smtp_mock.gemspec

@@ -22,7 +22,8 @@ Gem::Specification.new do |spec|
  'bug_tracker_uri' => 'https://github.com/mocktools/ruby-smtp-mock/issues'
  }
 
- dry_struct_version = ::Gem::Version.new(::RUBY_VERSION) >= ::Gem::Version.new('2.7.0') ? '~> 1.6' : '~> 1.4'
+ current_ruby_version = ::Gem::Version.new(::RUBY_VERSION)
+ dry_struct_version = current_ruby_version >= ::Gem::Version.new('2.7.0') ? '~> 1.6' : '~> 1.4'
 
  spec.required_ruby_version = '>= 2.5.0'
  spec.files = `git ls-files -z`.split("\x0").select { |f| f.match(%r{^(bin|lib|tmp)/|.ruby-version|smtp_mock.gemspec|LICENSE}) }
@@ -33,6 +34,7 @@ Gem::Specification.new do |spec|
  spec.add_runtime_dependency 'dry-struct', dry_struct_version
 
  spec.add_development_dependency 'ffaker', '~> 2.21'
+ spec.add_development_dependency 'net-smtp', '~> 0.3.3' if current_ruby_version >= ::Gem::Version.new('3.1.0')
  spec.add_development_dependency 'rake', '~> 13.0', '>= 13.0.6'
  spec.add_development_dependency 'rspec', '~> 3.12'
 end