message: Fixed a travis compiler issue
diff: @@ -19,7 +19,7 @@ matrix:
  - os: osx
  osx_image: xcode11.2
  env:
  - - MATRIX_EVAL="brew update && (brew outdated gcc7 || brew upgrade gcc7) && brew install gcc7 && CC=gcc-7 && CXX=g++-7"
  + - MATRIX_EVAL="brew update && (brew outdated gcc6 || brew upgrade gcc6) && brew install gcc6 && CC=gcc-6 && CXX=g++-6"
  before_install:
  - eval "${MATRIX_EVAL}"
  