ubuntu 18.04 install gitlab-ce

[安装指南](https://about.gitlab.com/install/#ubuntu)
tips: 注意，ubuntu's firefox 打开的网址中，安装推荐的是gitlab-ee；windows firefox 打开的网址中，安装推荐的是gitlab-ce

sudo apt-get install -y curl openssh-server ca-certificates
sudo apt-get install -y postfix
curl -sS https://packages.gitlab.com/install/repositories/gitlab/gitlab-ce/script.deb.sh | sudo bash
sudo EXTERNAL_URL="https://my ip address" apt-get install gitlab-ce