circleci: move yarn to apt-get

- Continue to use yarn instead of npm through ci pipeline to cache
things more

circle.yml

@@ -4,6 +4,9 @@ machine:
       - git config --global user.email "circleci@joyent.zone"
       - git config --global user.name "circlebot"
       - curl -sSL https://s3.amazonaws.com/circle-downloads/install-circleci-docker.sh | bash -s -- 1.10.0
+      - sudo apt-key adv --keyserver pgp.mit.edu --recv D101F7899D41F3C3
+      - echo "deb http://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
+      - sudo apt-get update && sudo apt-get install yarn
 
   timezone:
     Europe/London
@@ -16,10 +19,11 @@ machine:
 dependencies:
   cache_directories:
       - "/opt/circleci/nodejs/"
+      - "/home/ubuntu/.yarn-cache/"
       - "/opt/circleci/python/2.7.11/lib/python2.7/site-packages"
   pre:
       - pip --version && pip install --upgrade docker-compose==1.8.0
-      - npm install -g triton yarn
+      - yarn global add triton
       - echo '{"url":"https://eu-ams-1.api.joyent.com","account":"'$SDC_ACCOUNT'","keyId":"c3:30:35:9b:85:48:73:44:31:cc:4b:2e:6a:00:16:e2","name":"eu-ams-1","curr":true}' | triton profile create -f -
   post:
       - make install