Spandex.finish_{span,trace} don't update traces before completing

[GregMefford]

Maybe this was intentional, but while I was working on tests for the functions in the Spandex module, I noticed that if you pass in a completion_time when you call Spandex.finish_span, it is ignored. If you call Spandex.update_span with that option just before calling Spandex.finish_span, then it is updated. We should think about whether it makes sense to warn/log/error when you pass in unsupported opts that are going to get ignored.

[zachdaniel]

Yeah, I think it's just a bug that we don't update the span from the opts.

[zachdaniel]

Resolved by #88