Merge pull request #6626 from andreausu/add-slack-username

Change the notification sender username to GitLab in Slack Notifier

app/models/project_services/slack_service.rb

@@ -52,6 +52,7 @@ class SlackService < Service
     notifier = Slack::Notifier.new(subdomain, token)
     notifier.channel = room
+    notifier.username = 'GitLab'
     notifier.ping(message.compose)
   end