chore(spanner): update README file for benchwrapper
@@ -7,6 +7,6 @@ benchmarking code to prod at spanner without speaking Go.
```
cd spanner/internal/benchwrapper
-export SPANNER_EMULATOR_HOST=localhost:8080
+export SPANNER_EMULATOR_HOST=localhost:9010
go run *.go --port=8081
```
