message: Travis CI gcc version
diff: @@ -2,6 +2,20 @@ language: cpp
  sudo: required
  os: linux
  dist: trusty
  +matrix:
  + include:
  + # works on Precise and Trusty
  + - os: linux
  + addons:
  + apt:
  + sources:
  + - ubuntu-toolchain-r-test
  + packages:
  + - g++-7
  + env:
  + - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
  +before_install:
  + - eval "${MATRIX_EVAL}"
  compiler:
  - clang
  - gcc
  