fix: Gemspec/DevelopmentDependencies offense

Author: dennisklein

Gemfile

@@ -2,3 +2,12 @@
 
 source 'https://rubygems.org'
 gemspec
+
+group :test do
+  gem 'rake'
+  gem 'rspec'
+  gem 'rubocop'
+  gem 'rubocop-rake'
+  gem 'rubocop-rspec'
+  gem 'simplecov'
+end

ona.gemspec

@@ -10,11 +10,5 @@ Gem::Specification.new do |s|
   s.executables = ['ona.rb']
   s.homepage    = 'https://git.gsi.de/debian-packages/ruby-opennetadmin'
   s.license     = 'LGPL-3.0'
-  s.add_development_dependency 'rake'
-  s.add_development_dependency 'rspec'
-  s.add_development_dependency 'rubocop'
-  s.add_development_dependency 'rubocop-rake'
-  s.add_development_dependency 'rubocop-rspec'
-  s.add_development_dependency 'simplecov'
   s.metadata['rubygems_mfa_required'] = 'true'
 end