Twit now passes us an Error object, so use it

Per
https://github.com/ttezel/twit/blob/d729f0fd7be766945139425d2db838480b92
a66f/lib/oarequest.js#L211-L253
Merge pull request #6 from parkr/correct-error-handling-logic

Twit now passes us an Error object, so use it