Update Yarn version.

Author: jmdobry

circle.yml

@@ -19,9 +19,6 @@
 machine:
  node:
  version: 6.9.1
- environment:
- YARN_VERSION: 0.19.1
- PATH: "${PATH}:${HOME}/.yarn/bin:${HOME}/${CIRCLE_PROJECT_REPONAME}/node_modules/.bin"
  services:
  - redis
  - memcached
@@ -35,18 +32,13 @@ general:
 # Install your project's language-specific dependencies
 dependencies:
  pre:
- - |
- if [[ ! -e ~/.yarn/bin/yarn || $(yarn --version) != "${YARN_VERSION}" ]]; then
- curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version $YARN_VERSION
- fi
  - yarn global add nyc codecov
  override:
- - yarn install
+ - yarn
  post:
  - echo $KEYFILE > /home/ubuntu/nodejs-docs-samples/key.json
  - node scripts/install
  cache_directories:
- - ~/.yarn
  - ~/.cache/yarn
  - appengine/bower/node_modules
  - appengine/cloudsql/node_modules