docs/readme: Fix goreport url
## storage
[![Build Status](https://travis-ci.com/Xuanwo/storage.svg?branch=master)](https://travis-ci.com/Xuanwo/storage)
-[![Go Report Card](https://goreportcard.com/badge/github.com/Xuanwo/storage)](https://goreportcard.com/badge/github.com/Xuanwo/storage)
+[![Go Report Card](https://goreportcard.com/badge/github.com/Xuanwo/storage)](https://goreportcard.com/report/github.com/Xuanwo/storage)
[![License](https://img.shields.io/badge/license-apache%20v2-blue.svg)](https://github.com/Xuanwo/storage/blob/master/LICENSE)
A unified storage layer for Golang.
