Add bundler-audit to keep the gem secure

Rakefile

@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 
+require 'bundler/audit/task'
 require 'bundler/gem_tasks'
 require 'rspec/core/rake_task'
-
-RSpec::Core::RakeTask.new(:spec)
-
 require 'rubocop/rake_task'
 
+Bundler::Audit::Task.new
+RSpec::Core::RakeTask.new(:spec)
 RuboCop::RakeTask.new
 
 task default: %i[spec rubocop]

nostr.gemspec

@@ -31,6 +31,7 @@ Gem::Specification.new do |spec|
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
+  spec.add_development_dependency 'bundler-audit', '~> 0.9'
   spec.add_development_dependency 'overcommit', '~> 0.59'
   spec.add_development_dependency 'rake', '~> 13.0'
   spec.add_development_dependency 'rspec', '~> 3.12'