message: Use GitHub releases for libcouchbase 2 on linux
diff: add_couchbase_libs() {
  if [ "$(uname -s)" = "Linux" ]; then
  if [[ ${version:?} =~ 5.[3-6]|7.[0-1] ]]; then
  - trunk="http://packages.couchbase.com/ubuntu"
  - list="deb $trunk ${DISTRIB_CODENAME:?} ${DISTRIB_CODENAME:?}/main"
  + release="2.10.9"
  + trunk="https://github.com/couchbase/libcouchbase/releases/download"
  + package="libcouchbase-${release}_ubuntu${DISTRIB_RELEASE/./}_${DISTRIB_CODENAME}_amd64.tar"
  + get -q -n /tmp/libcouchbase.tar "$trunk/$release/$package"
  + sudo tar -xf /tmp/libcouchbase.tar -C /tmp
  + install_packages libev4
  + sudo dpkg -i /tmp/libcouchbase-*/*.deb
  else
  trunk="http://packages.couchbase.com/clients/c/repos/deb"
  list="deb $trunk/ubuntu${DISTRIB_RELEASE/./} ${DISTRIB_CODENAME:?} ${DISTRIB_CODENAME:?}/main"
  - fi
  - add_pecl
  get -s -n "" "$trunk/couchbase.key" | sudo apt-key add
  echo "$list" | sudo tee /etc/apt/sources.list.d/couchbase.list
  sudo apt-get update
  + fi
  ${apt_install:?} libcouchbase-dev
  else
  if [[ ${version:?} =~ 5.[3-6]|7.[0-1] ]]; then
  