message: travis: switched to using gcc 9
diff: @@ -14,12 +14,12 @@ if [ "$TRAVIS_OS_NAME" = "osx" ]; then
  fi
  if [ "$TRAVIS_OS_NAME" = "linux" ]; then
  - # Link gcc-7 and g++-7 to their standard commands
  - sudo ln -s /usr/bin/gcc-7 /usr/local/bin/gcc
  - sudo ln -s /usr/bin/g++-7 /usr/local/bin/g++
  + # Link gcc-9 and g++-9 to their standard commands
  + sudo ln -s /usr/bin/gcc-9 /usr/local/bin/gcc
  + sudo ln -s /usr/bin/g++-9 /usr/local/bin/g++
  # Export CC and CXX to tell cmake which compiler to use
  - export CC=/usr/bin/gcc-7
  - export CXX=/usr/bin/g++-7
  + export CC=/usr/bin/gcc-9
  + export CXX=/usr/bin/g++-9
  # Check versions of gcc, g++ and cmake
  gcc -v
  g++ -v
  