This is how I am compliling Openvpn 2.7 on unbutu 18 if you like you can try it .
sudo apt remove openvpn
sudo apt install build-essential
sudo apt-get install libssl-dev liblzo2-dev libpam0g-dev
sudo apt install git curl wget libnewt-dev libssl-dev libncurses5-dev subversion libsqlite3-dev build-essential libjansson-dev libxml2-dev uuid-dev
sudo add-apt-repository universe
sudo apt update
sudo apt install subversion
curl -o openvpn-2.5.7.tar.gz https://swupdate.openvpn.org/community/releases/openvpn-2.5.7.tar.gz
tar -xf openvpn-2.5.7.tar.gz
cd openvpn-2.5.7
sudo ./configure
sudo make
sudo make install
