refactor(docs): update badge

README.md

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-# bimg [![Build Status](https://travis-ci.org/h2non/bimg.png)](https://travis-ci.org/h2non/bimg) [![GitHub release](https://img.shields.io/github/tag/h2non/bimg.svg)](https://github.com/h2non/bimg/releases) [![GoDoc](https://godoc.org/github.com/h2non/bimg?status.png)](https://godoc.org/github.com/h2non/bimg) [![Coverage Status](https://coveralls.io/repos/h2non/bimg/badge.svg?branch=master)](https://coveralls.io/r/h2non/bimg?branch=master)
+# bimg [![Build Status](https://travis-ci.org/h2non/bimg.png)](https://travis-ci.org/h2non/bimg) [![GitHub release](https://img.shields.io/github/tag/h2non/bimg.svg)](https://github.com/h2non/bimg/releases) [![GoDoc](https://godoc.org/github.com/h2non/bimg?status.svg)](https://godoc.org/github.com/h2non/bimg) [![Coverage Status](https://coveralls.io/repos/h2non/bimg/badge.svg?branch=master)](https://coveralls.io/r/h2non/bimg?branch=master)
 
 Small [Go](http://golang.org) library for blazing fast and efficient image processing based on [libvips](https://github.com/jcupitt/libvips) using C bindings. It provides a clean, simple and fluent [API](https://godoc.org/github.com/h2non/bimg) in pure Go.