Fixes three Zipkin v2 swagger2 datatypes

[philipbawn]

This PR allows some client generators (such as nswag) to select the correct data type for microseconds when either:

1. querying for spans, or
2. de-serializing timestamps in annotations

This PR author is not sure if all client or server generators behave the same. For those that have never queried for a long span and weren't otherwise having problems this could break something somewhere for someone even though it improves zipkin-api.

[philipbawn]

I don't think maven likes the yaml comments unless it is the license year that is the problem. Also I read the contributor instructions, is there a more appropriate branch to PR against?

Thanks, Philip

[devinsba]

You'll just want to update the end date on the license header. Sorry, this isn't documented because it only happens once a year.