.travis.yml

language: node_js
os:
    - linux
    - osx
sudo: required
osx_image: xcode9.4
node_js:
    - "stable"
before_install:
    - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update                          ; fi
    - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install gcc || echo "done."     ; fi
    - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew link --overwrite gcc            ; fi
    - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install r                       ; fi
    - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then echo "deb https://cloud.r-project.org/bin/linux/ubuntu trusty-cran35/" | sudo tee -a /etc/apt/sources.list ; fi
    - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get update                 ; fi
    - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get install r-base -y --allow-unauthenticated      ; fi
    - R --version