Update .travis.yml

.travis.yml

@@ -1,3 +1,12 @@
+before_install: # if "install" is overridden
+  # Repo for Yarn
+  - sudo apt-key adv --fetch-keys http://dl.yarnpkg.com/debian/pubkey.gpg
+  - echo "deb http://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
+  - sudo apt-get update -qq
+  - sudo apt-get install -y -qq yarn
+cache:
+  yarn: true
+
 matrix:
   include:
     - os: osx
@@ -18,16 +27,11 @@ cache:
     - $HOME/.cache/electron
     - $HOME/.cache/electron-builder
 
-before_script:
-  - yarn install
-
 script:
   - |
     if [ "$TRAVIS_OS_NAME" == "linux" ]; then
       docker run --rm \
         --env-file <(env | grep -vE '\r|\n' | grep -iE 'DEBUG|NODE_|ELECTRON_|YARN_|NPM_|CI|CIRCLE|TRAVIS_TAG|TRAVIS|TRAVIS_REPO_|TRAVIS_BUILD_|TRAVIS_BRANCH|TRAVIS_PULL_REQUEST_|APPVEYOR_|CSC_|GH_|GITHUB_|BT_|AWS_|STRIP|BUILD_') \
-        --env ELECTRON_CACHE="/root/.cache/electron" \
-        --env ELECTRON_BUILDER_CACHE="/root/.cache/electron-builder" \
         -v ${PWD}:/project \
         -v ~/.cache/electron:/root/.cache/electron \
         -v ~/.cache/electron-builder:/root/.cache/electron-builder \