rds: rename shadowing to request mirroring. (#53)
rds: rename shadowing to request mirroring. (#53)

This was a clarification suggested by @amb67, since traffic mirroring is a well known term but shadowing less so.
lyft/envoy-api,rshriram/envoy-api,lyft/envoy-api,jrajahalme/envoy-api,lyft/envoy-api,rshriram/envoy-api,jrajahalme/envoy-api,jrajahalme/envoy-api,rshriram/envoy-api,jrajahalme/envoy-api