Pre-Built Packages for Mainline version on nginx.org:
http://nginx.org/en/linux_packages.html#mainline

Warning: The nginx.org repository does not currently support Ubuntu 18.04. Support for Bionic should be available soon.

This will get you the latest version of Nginx. Use this version if you are a pro and if you really need the most actual Nginx build, as it may lack some Ubuntu specific integration and tweaks.

Download and add the PGP key to authenticate the Nginx repository signature:
wget -qO - https://nginx.org/keys/nginx_signing.key | sudo apt-key add -

Append the repositories to the end of the /etc/apt/sources.list file:

echo “deb http://nginx.org/packages/mainline/ubuntu/ bionic nginx” | sudo tee -a /etc/apt/sources.list

echo “deb-src http://nginx.org/packages/mainline/ubuntu/ bionic nginx” | sudo tee -a /etc/apt/sources.list

Update and install:
sudo apt update && sudo apt install nginx