heartcheck.gemspec in heartcheck-1.0.7 vs heartcheck.gemspec in heartcheck-1.0.8

@@ -25,6 +25,7 @@
   spec.add_development_dependency 'rubocop', '~> 0.27.0', '>= 0.27.1'
   spec.add_development_dependency 'thor', '~> 0.19.0', '>= 0.19.1'
   spec.add_development_dependency 'rack-test', '~> 0.6.0', '>= 0.6.3'
   # for documentation
   spec.add_development_dependency 'yard', '~> 0.8.0', '>= 0.8.7.6'
+  spec.add_development_dependency 'concurrent-ruby', '~> 0.9.1', '>= 0.9.1'
 end