Changed to use the <Message> resource URI rather than the old <SMS> one

The resource URI used in the module code doesn't allow text messages longer than 160 chars and actually deprecated according to  https://www.twilio.com/help/faq/sms/does-twilio-support-concatenated-sms-messages-or-messages-over-160-characters
Therefore I have updated the code to use the new URI recommended for messages