Merge pull request #587 from y-yagi/add_logger_as_dependency

Add `logger` gem as a runtime dependency

Author: rymai

listen.gemspec

@@ -34,6 +34,7 @@ Gem::Specification.new do |gem| # rubocop:disable Metrics/BlockLength
 
   gem.required_ruby_version = '>= 2.4.0' # rubocop:disable Gemspec/RequiredRubyVersion
 
+  gem.add_dependency 'logger'
   gem.add_dependency 'rb-fsevent', '~> 0.10', '>= 0.10.3'
   gem.add_dependency 'rb-inotify', '~> 0.9', '>= 0.9.10'
 end