message: Use ccache with Travis
  Enable ccache caching in Travis builds.
diff: @@ -34,11 +34,11 @@ addons:
  - libsecret-1-dev
  env:
  - - REAL_CC=gcc-6 REAL_CXX=g++-6
  + - REAL_CC='ccache gcc-6' REAL_CXX='ccache g++-6'
  before_install:
  # work around Travis being difficult, see https://github.com/travis-ci/travis-ci/issues/6633
  - - export CC=$REAL_CC CXX=$REAL_CXX
  + - export CC="$REAL_CC" CXX="$REAL_CXX"
  # git submodules needed for Linux:
  - git submodule update --init deps/json deps/pugixml
  @@ -53,7 +53,9 @@ after_failure:
  git:
  submodules: false
  -cache: apt
  +cache:
  + apt: true
  + ccache: true
  deploy:
  provider: releases
  