message: fixed unzip in old travis macOS image
diff: @@ -21,6 +21,11 @@ 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
  