Cache APT packages

.travis.yml

# .travis.yml
# inspired by https://stackoverflow.com/a/52446551

sudo: required
dist: trusty

language: scala
scala: 2.12.8

before_cache:
  - sudo chown -R $USER ${TRAVIS_BUILD_DIR}/apt-cache
  
cache:
  directories:
    - $TRAVIS_BUILD_DIR/.ivy2   # to avoid always download the same stuff from maven central
    - apt-cache

before_install:
  - |
    if [ ! -f ${TRAVIS_BUILD_DIR}/apt-cache/pkgcache.bin ]; then
       mkdir -p ${TRAVIS_BUILD_DIR}/apt-cache/archives/partial
       mkdir -p ${TRAVIS_BUILD_DIR}/apt-cache/partial
       mkdir -p ${TRAVIS_BUILD_DIR}/apt-cache/lists
       sudo apt-get -y -o Dir::cache=${TRAVIS_BUILD_DIR}/apt-cache -o Dir::State::Lists=${TRAVIS_BUILD_DIR}/apt-cache/lists update
       sudo apt-get install --download-only -o Dir::cache=${TRAVIS_BUILD_DIR}/apt-cache -o Dir::State::Lists=${TRAVIS_BUILD_DIR}/apt-cache/lists texlive-full texlive-latex-extra texlive-lang-all texlive-lang-swedish
    fi
  - sudo apt-get install --no-download -o Dir::cache=${TRAVIS_BUILD_DIR}/apt-cache -o Dir::State::Lists=${TRAVIS_BUILD_DIR}/apt-cache/lists texlive-full texlive-latex-extra texlive-lang-all texlive-lang-swedish

script:
  - sbt build