message: [travis] Add Boost 1.67.0 to Travis image
diff: set -eux
  -BOOST_VERSIONS=(1.61.0 1.62.0 1.63.0 1.64.0 1.65.1 1.66.0)
  +BOOST_VERSIONS=(1.61.0 1.62.0 1.63.0 1.64.0 1.65.1 1.66.0 1.67.0)
  BOOST_LIBRARIES="chrono,date_time,python,system,test,thread"
  BUILD_ROOT=/tmp/boosts
  