Upgrade Twilio SMS API #110
Description
Twilio removed the deprecated SMS/Messages API endpoint, replacing it with a new /Messages one, so Nuntium AOs to Twilio now fail with Twilio::REST::RequestError - Method not allowed (as of Nuntium 1.14.0).
We should upgrade to the new API, either by upgrading the twilio-ruby gem (which now requires Ruby >= 2.0 - and Nuntium is still in 1.9), or by manually performing the few API requests Nuntium does.