Change docker backup command in readme

doc/raketasks/backup_restore.md

@@ -32,7 +32,7 @@ sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
 ```
 If you are running GitLab within a Docker container, you can run the backup from the host:
 ```
-docker -t exec <container name> gitlab-rake gitlab:backup:create
+docker exec -t <container name> gitlab-rake gitlab:backup:create
 ```
 
 You can specify that portions of the application data be skipped using the