Revert "Remove gem signing so I can push"

This reverts commit 285d35a.

Author: parndt

awesome_nested_set.gemspec

@@ -26,4 +26,9 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'pry-nav'
   s.add_development_dependency 'rake', '~> 13'
   s.add_development_dependency 'rspec-rails', '>= 4.0.0', '<= 6.2'
+
+  s.cert_chain = [File.expand_path('certs/parndt.pem', __dir__)]
+  if $PROGRAM_NAME =~ /gem\z/ && ARGV.include?('build') && ARGV.include?(__FILE__)
+    s.signing_key = File.expand_path('~/.ssh/gem-private_key.pem')
+  end
 end