message: using latest default image version for linux and macOS in travis build
diff: @@ -8,12 +8,9 @@ matrix:
  - env: os_build=android os_arch=x86_64 android_api=21
  - env: os_build=linux os_arch=x86
  - env: os_build=linux os_arch=x86_64
  - - dist: trusty
  - env: os_build=windows os_arch=x86
  - - dist: trusty
  - env: os_build=windows os_arch=x86_64
  + - env: os_build=windows os_arch=x86
  + - env: os_build=windows os_arch=x86_64
  - os: osx
  - osx_image: xcode7.3
  env: os_build=macosx os_arch=x86_64
  branches:
  @@ -21,11 +18,6 @@ branches:
  - master
  before_install:
  -# fix unzip in macOS until we can move to a higher version
  - - if [ $os_build == "macosx" ]; then
  - brew update > /dev/null && brew install --quiet unzip;
  - export PATH="/usr/local/opt/unzip/bin:$PATH";
  - fi
  # boost: download and bootstrap
  - wget -nv -O boost.zip https://dl.bintray.com/boostorg/release/1.68.0/source/boost_1_68_0.zip
  - unzip -qq boost.zip
  