message: Add gcc-9 to use with travis-CI
diff: @@ -63,6 +63,20 @@ matrix:
  - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
  compiler: g++-8
  + - os: linux
  + addons:
  + apt:
  + sources:
  + - ubuntu-toolchain-r-test
  + packages:
  + - g++-9
  + - ninja-build
  + - xorg-dev
  + - libglu1-mesa-dev
  + env:
  + - MATRIX_EVAL="CC=gcc-9 && CXX=g++-9"
  + compiler: g++-9
  +
  - os: linux
  before_install:
  - sudo apt-get update
  