README: update badges

Signed-off-by: Gyu-Ho Lee <[email protected]>

README.md

@@ -1,10 +1,12 @@
 # etcd
 
-[![Go Report Card](https://goreportcard.com/badge/github.com/coreos/etcd)](https://goreportcard.com/report/github.com/coreos/etcd)
+[![Go Report Card](https://goreportcard.com/badge/github.com/coreos/etcd?style=flat-square)](https://goreportcard.com/report/github.com/coreos/etcd)
 [![Coverage](https://codecov.io/gh/coreos/etcd/branch/master/graph/badge.svg)](https://codecov.io/gh/coreos/etcd)
-[![Build Status](https://travis-ci.org/coreos/etcd.svg?branch=master)](https://travis-ci.org/coreos/etcd)
-[![Build Status](https://semaphoreci.com/api/v1/coreos/etcd/branches/master/shields_badge.svg)](https://semaphoreci.com/coreos/etcd)
-[![Docker Repository on Quay.io](https://quay.io/repository/coreos/etcd-git/status "Docker Repository on Quay.io")](https://quay.io/repository/coreos/etcd-git)
+[![Build Status Travis](https://img.shields.io/travis/coreos/etcdlabs.svg?style=flat-square&&branch=master)](https://travis-ci.org/coreos/etcd)
+[![Build Status Semaphore](https://semaphoreci.com/api/v1/coreos/etcd/branches/master/shields_badge.svg)](https://semaphoreci.com/coreos/etcd)
+[![Godoc](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](https://godoc.org/github.com/coreos/etcd)
+[![Releases](https://img.shields.io/github/release/coreos/etcd/all.svg?style=flat-square)](https://github.com/coreos/etcd/releases)
+[![LICENSE](https://img.shields.io/github/license/coreos/etcd.svg?style=flat-square)](https://github.com/coreos/etcd/blob/master/LICENSE)
 
 **Note**: The `master` branch may be in an *unstable or even broken state* during development. Please use [releases][github-release] instead of the `master` branch in order to get stable binaries.