Replace XHR with window.fetch (polyfill)

[parasyte]

• Documentation: https://developers.google.com/web/updates/2015/03/introduction-to-fetch
• Polyfill: https://github.com/github/fetch
• Dependency (Promises polyfill): https://github.com/jakearchibald/es6-promise

[obiot]

love this one !