Added fix for Auth.prototype.checkBodyIsObject yielding false positive

Hi I've added a fix for the method Auth.prototype.checkBodyIsObject yielding a false positive when the parsedBody param is an array.  I discovered this when working with Twitter OAuth1.0A authentication and as such have added a test for the Use Case that it implements under test/twitter.js.

It would be great if you could accept the changes and redeploy to NPM.

Cheers

Pat