Hi all, it seems that Bintray does not support the HTTP protocol with apt-get anymore. I will edit the docs to reflect this change:
You may install using the following commands:
sudo apt-get install apt-transport-https
echo 'deb https://dl.bintray.com/openhab/apt-repo2 stable main' | sudo tee /etc/apt/sources.list.d/openhab2.list
sudo apt-get update
sudo apt-get install openhab2