Adjust code coverage badge

README.md

@@ -5,7 +5,7 @@ A reasonably complete and well-tested golang port of [Kenneth Reitz][kr]'s
 
 [![GoDoc](https://godoc.org/github.com/mccutchen/go-httpbin?status.svg)](https://godoc.org/github.com/mccutchen/go-httpbin)
 [![Build Status](https://travis-ci.org/mccutchen/go-httpbin.svg?branch=master)](http://travis-ci.org/mccutchen/go-httpbin)
-[![Coverage](http://gocover.io/_badge/github.com/mccutchen/go-httpbin/httpbin?0)](http://gocover.io/github.com/mccutchen/go-httpbin/httpbin)
+[![Coverage](https://codecov.io/gh/mccutchen/go-httpbin/branch/master/graph/badge.svg)](https://codecov.io/gh/mccutchen/go-httpbin)
 
 
 ## Usage