upgrade gitlab

Steps:

curl https://packages.gitlab.com/gpg.key -o /tmp/omnibus_gitlab_gpg.key
sudo apt-key add /tmp/omnibus_gitlab_gpg.key
sudo apt update
sudo apt-get install gitlab-ce
sudo SKIP_POST_DEPLOYMENT_MIGRATIONS=true gitlab-ctl reconfigure
sudo gitlab-rake db:migrate
sudo gitlab-ctl hup unicorn
sudo gitlab-ctl hup puma
sudo gitlab-ctl restart sidekiq

refer to zero-downtime-updates