Slack integration does not work in 6.9

In version 6.9 slack integration does not work and returns error 500:

Started GET "/group/project/services/slack/test" for 127.0.0.1 at 2014-05-23 19:47:29 +0200
Processing by Projects::ServicesController#test as HTML
  Parameters: {"project_id"=>"group/project", "id"=>"slack"}
Completed 500 Internal Server Error in 538ms

OpenSSL::SSL::SSLError (hostname does not match the server certificate):
  app/models/project_services/slack_service.rb:57:in `execute'
  app/controllers/projects/services_controller.rb:29:in `test'
  app/controllers/application_controller.rb:59:in `set_current_user_for_thread'


Started GET "/group/project/services/slack/test" for 127.0.0.1 at 2014-05-23 19:47:29 +0200
Processing by Projects::ServicesController#test as HTML
  Parameters: {"project_id"=>"group/project", "id"=>"slack"}
Completed 500 Internal Server Error in 375ms

OpenSSL::SSL::SSLError (hostname does not match the server certificate):
  app/models/project_services/slack_service.rb:57:in `execute'
  app/controllers/projects/services_controller.rb:29:in `test'
  app/controllers/application_controller.rb:59:in `set_current_user_for_thread'

Skipping SSL verification in slack notifies (by adding http.verify_mode = OpenSSL::SSL::VERIFY_NONE in slack-notifier/http_post.rb) results in no error, but no notification is sent. Using github integration via Web hooks works