Merge branch 'blackst0ne-rails5-fix-frozen-array' into 'master'

[Rails5] Fix `can't modify frozen Array` errors

See merge request gitlab-org/gitlab-ce!18239

app/services/notification_recipient_service.rb

@@ -54,8 +54,7 @@ module NotificationRecipientService
           users = users.includes(:notification_settings)
         end
-        users = Array(users)
-        users.compact!
+        users = Array(users).compact
         recipients.concat(users.map { |u| make_recipient(u, type, reason) })
       end