Zipkin updates + Axios #41
Description
- Zipkin instrumentation now has a separate axios package: https://github.com/openzipkin/zipkin-js/tree/master/packages/zipkin-instrumentation-axiosjs
- Zipkin has a Koa implementation: https://github.com/uswitch/zipkin-instrumentation-koa
- Zipkin also now has different options as of 0.19.0