travis: Use Ubuntu LTS Bionic

instead of the older LTS Xenial, which is the default on Travis.

This allows to remove upgrade docker from docker upstream repository for
new distros (openSUSE Tumbleweed, Fedora), which speedup the build.

Signed-off-by: Petr Vorel <[email protected]>

Author: pevik

.travis.yml

@@ -1,5 +1,6 @@
 # Copyright (c) 2017-2020 Petr Vorel <[email protected]>
 
+dist: bionic
 sudo: required
 language: c
 services:
@@ -101,14 +102,4 @@ script:
     - if [ "$MAKE_INSTALL" = 1 ]; then INSTALL_OPT="-i"; fi
     - if [ ! "$TREE" ]; then TREE="in"; fi
     - case $VARIANT in cross-compile*) BUILD="cross";; i386) BUILD="32";; *) BUILD="native";; esac
-
-    # Tumbleweed requires newer Docker version
-    - >
-        if [ "${DISTRO//*\/}" = "tumbleweed" -o "$INSTALL" = "fedora" ]; then
-            curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
-            sudo add-apt-repository "deb [arch=$(dpkg --print-architecture)] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
-            sudo apt-get update
-            sudo apt-get -y -o Dpkg::Options::="--force-confnew" install docker-ce
-        fi
-
     - docker run -t ltp /bin/sh -c "cd travis && ./$INSTALL.sh && if [ \"$VARIANT\" ]; then ARCH=\"$ARCH\" ./$INSTALL.$VARIANT.sh; fi && ../build.sh -o $TREE -t $BUILD -c $CC $INSTALL_OPT"