I've recently created a new droplet with Ubuntu 16.04 and was pleased to see that sudo apt-get install apache2 gets me Apache 2.4.18. I was hoping that would allow me to enable HTTP2 support; alas, the respe...
Another option is using Ondrej's Launchpad PPA (https://launchpad.net/~ondrej/+archive/ubuntu/apache2).
For example: (replacing REPOSITORY with string from that page for your Ubuntu version).
sudo add-apt-repository ...