Merge pull request #93 from JulianHn/lsb-cleanup

Replace lsb_release call with parsing /etc/os-release

.travis/before_install.sh

@@ -12,7 +12,7 @@ if [ ! -z ${TRAVIS:-} ] ; then
         if ${DOCKER:-false} ; then
             echo "Installing Docker"
             curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
-            sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
+            sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(grep -Po 'VERSION_CODENAME=\K.*' /etc/os-release) stable"
             sudo apt-get update
             sudo apt-get -y install docker-ce
         fi