Respect globs array order, fixes #25

Fixes #25
Fixes gulpjs/gulp#837
About the one-liner: I've put it in a single line for consistency with [this line below](https://github.com/wearefractal/glob-stream/pull/27/files#diff-168726dbe96b3ce427e7fedce31bb0bcR89). Should I just add some line breaks in the middle of the expression or create unnecessary temp vars?

About `length === 1`: AFAICS the same perf benefit still holds after this patch. That is, although the globs are now ordered, the file emission order inside each individual stream remains unordered. I don't quite see why this optimization should be removed now.