Add codecov.io badge

Author: leonelquinteros

README.md

@@ -1,5 +1,6 @@
 [![GoDoc](https://godoc.org/github.com/leonelquinteros/gotext?status.svg)](https://godoc.org/github.com/leonelquinteros/gotext)
 [![Build Status](https://travis-ci.org/leonelquinteros/gotext.svg?branch=master)](https://travis-ci.org/leonelquinteros/gotext)
+[![codecov](https://codecov.io/gh/leonelquinteros/gotext/branch/master/graph/badge.svg)](https://codecov.io/gh/leonelquinteros/gotext)
 [![Go Report Card](https://goreportcard.com/badge/github.com/leonelquinteros/gotext)](https://goreportcard.com/report/github.com/leonelquinteros/gotext)
 
 # Gotext
@@ -19,7 +20,7 @@ Version: [v1.1.1](https://github.com/leonelquinteros/gotext/releases/tag/v1.1.1)
   - Support for [message contexts](https://www.gnu.org/software/gettext/manual/html_node/Contexts.html).
 - Thread-safe: This package is safe for concurrent use across multiple goroutines. 
 - It works with UTF-8 encoding as it's the default for Go language.
-- Unit tests available. See coverage: https://gocover.io/github.com/leonelquinteros/gotext
+- Unit tests available.
 - Language codes are automatically simplified from the form `en_UK` to `en` if the first isn't available.
 - Ready to use inside Go templates.