Fix path in go helloworld docs
@ -16,8 +16,8 @@ INSTALL
-------
```sh
$ go get -u github.com/grpc-common/go/greeter_client
$ go get -u github.com/grpc-common/go/greeter_server
$ go get -u github.com/grpc/grpc-common/go/greeter_client
$ go get -u github.com/grpc/grpc-common/go/greeter_server
```
TRY IT!