Multiple failures in Elixir 1.2

[victorolinasc]

I would like some feedback as to how we should handle multiple failures in one test.

As of Elixir 1.2, user of ExUnit can fire multiple failures in one test. This broke this library initially and @adrienmo pulled a fix (thanks a lot :D). The issue is that our solution is simply using the first failure when it receives a list of failures.

My worries about producing an XML with several failure nodes is with tools that consume this report. Will they break? They SHOULD NOT as it will still be valid XML, but not sure the results will be accounted.

Anyway, more feedback on this is much appreciated 👍