Chai-as-promised breaks in Browserify since it includes BOM at the start of the file stream

This is actually a problem in Browserify (or some of its dependencies, didn't analyse yet) (see substack/node-browserify#313), which keeps the BOM markers when bundling the stream, however it hasn't been fixed in months, and @substack hasn't commented on that issue himself.

At any rate, I don't think the library uses anything by removing the marker, and by removing it it'll work on Browserify and Testling CI, so...