message: Add build status badge to readme
diff: # html2js
  +[![Build Status](https://travis-ci.com/Polymer/html2js.svg?token=x6MxFyUe7PYM8oPW9m6b&branch=master)](https://travis-ci.com/Polymer/html2js)
  +
  html2js is a tool to convert packages of HTML imports to JavaScript modules.
  ## Goals
  