Below are my build instructions for GnuPG 2.1.13 released on June 16th, 2016. These instructions are built for a headless Ubuntu 14.04 LTS server (and have also been tested on Ubuntu 15.10 and 16.04).
Or if you wish, you may use the install script to install GnuPG 2.1.13 by running the following script:
curl -OL "https://gist.github.com/vt0r/a2f8c0bcb1400131ff51/raw/b2981d72edd7ba14dda00a57860228972d2e7f96/install-gnupg21.sh" && sudo bash ./install-gnupg21.sh