rename `specs` to `routes`

[michelleN]

https://github.com/deislabs/smi-spec/blob/master/traffic-specs.md

If you replace specs with routes in the traffic access example, it becomes more readable and intuitive.

[grampelberg]

The original idea with specs was to have it work for things that aren't routes such as SQL queries, kafka queues, ....

Since the only thing that lives in there now is routes, maybe a little blurb at the bottom about this being a pattern usable by other protocols?