polymer-cli: travis and package.json templates

.travis.yml

language: node_js
sudo: required
install: yarn install
node_js: '6'
addons:
  firefox: latest
  apt:
    sources:
    - google-chrome
    packages:
    - google-chrome-stable
script: yarn test
dist: trusty

package.json

{
  "scripts": {
    "install": "node_modules/.bin/polymer install",
    "test": "node_modules/.bin/polymer test"
  },
  "devDependencies": {
    "polymer-cli": "^0.18.0-pre.13",
    "web-component-tester": "^6.0.0-prerelease.7"
  }
}