message: chore(publish): use Travis CI `deploy` configuration
  Rather than using the `after_success` hook, which runs on all hosts and keeps the first one running until all of them are done, we use the `deploy` hook to run the publishing steps and restrict them to just the `master` branch.
diff: sudo: false
  language: node_js
  +
  cache:
  yarn: true
  directories:
  - node_modules
  +
  notifications:
  email: false
  +
  before_install:
  - yarn global add greenkeeper-lockfile@1
  before_script:
  - greenkeeper-lockfile-update
  after_script:
  - greenkeeper-lockfile-upload
  +
  node_js:
  - '9'
  - '8'
  - '6'
  - '4'
  -after_success:
  - - 'curl -Lo travis_after_all.py https://git.io/travis_after_all'
  - - python travis_after_all.py
  - - export $(cat .to_export_back) &> /dev/null
  - - semantic-release pre && yarn run build && npm publish && semantic-release post
  - - npm run update-website
  +
  +deploy:
  + # Publish to NPM.
  + - provider: script
  + script: semantic-release pre && yarn build && npm publish && semantic-release post
  + on:
  + branch: master
  + # Update the website.
  + - provider: script
  + script: yarn update-website
  + on:
  + branch: master
  +
  branches:
  except:
  - /^v\d+\.\d+\.\d+$/
  