message: travis: use MATRIX_EVAL to properly get env vars
  This also switches the deploy build to the default gcc version.
diff: @@ -8,7 +8,7 @@ matrix:
  sudo: false
  compiler: gcc
  env:
  - - BUILD_TARGET=gcc_build
  + - MATRIX_EVAL="BUILD_TARGET=gcc_build && DEPLOY_BUILD=yes"
  addons:
  apt:
  packages:
  @@ -18,9 +18,7 @@ matrix:
  sudo: false
  compiler: gcc
  env:
  - - BUILD_TARGET=gcc_build
  - - CC=gcc-5
  - - CXX=g++-5
  + - MATRIX_EVAL="BUILD_TARGET=gcc_build && CC=gcc-5 && CXX=g++-5"
  addons:
  apt:
  sources:
  @@ -34,10 +32,7 @@ matrix:
  sudo: false
  compiler: gcc
  env:
  - - BUILD_TARGET=coverage_build
  - - DEPLOY_BUILD=yes
  - - CC=gcc-6
  - - CXX=g++-6
  + - MATRIX_EVAL="BUILD_TARGET=coverage_build && CC=gcc-6 && CXX=g++-6"
  addons:
  apt:
  sources:
  @@ -62,6 +57,7 @@ addons:
  - libcurl4-openssl-dev
  before_install:
  +- eval "${MATRIX_EVAL}"
  - if [[ "${BUILD_TARGET}" = "coverage_build" ]]; then
  pip install --user cpp-coveralls;
  fi
  