Fix broken unit test

`grpc_handler_test.go` has syntax error.

```
# 0chain.net/blobbercore/handler [0chain.net/blobbercore/handler.test]
./grpc_handler_test.go:39:35: not enough arguments in call to NewServerWithMiddlewares
	have ()
	want ("github.com/grpc-ecosystem/go-grpc-middleware/ratelimit".Limiter)
FAIL	0chain.net/blobbercore/handler [build failed]
```