visionmedia/superagent — pull request #511 by dmartinezg (2014-12-16 12:20:01+00:00)
Title: Fix call to form-data, to allow the setting of filenames in the attachment

If you check https://github.com/felixge/node-form-data/blob/master/lib/form_data.js#L151

form-data append expects the third parameter to be an `options` object which _may_ have a `filename` property .