Fixes new VIES response XML parsing

• explicitly passes a content-type header when POSTing to VIES
• changes the XML namespace prefixes so xpath can correctly access values (also updates fixtures with new VIES responses)
• adds better handling when SweetXml is errors during xpath calls

0.1.5

Ensure VIES client URL is using https (#7)

* Ensure VIES client URL is using https

* Fix credo warning for variable name location

0.1.4 - Update URL to use https (#6)

* Update changelog and version

* Update url to https to avoid invalid XML redirect

* Update readme to account for latest version