Fix gRPC README in examples (#628)

Author: wapa5pow

examples/grpc/README.md

@@ -27,5 +27,5 @@ You will see traces and stats exported on the stdout. You can use one of the
 to upload collected data to the backend of your choice.
 
 You can also see the z-pages provided from the server:
-* Traces: http://localhost:8081/tracez
-* RPCs: http://localhost:8081/rpcz
+* Traces: http://localhost:8081/debug/tracez
+* RPCs: http://localhost:8081/debug/rpcz