Switch from png to svg for GoDoc link in README

README.md

@@ -1,7 +1,7 @@
 sarama
 ======
 
-[![GoDoc](https://godoc.org/github.com/Shopify/sarama?status.png)](https://godoc.org/github.com/Shopify/sarama)
+[![GoDoc](https://godoc.org/github.com/Shopify/sarama?status.svg)](https://godoc.org/github.com/Shopify/sarama)
 [![Build Status](https://travis-ci.org/Shopify/sarama.svg?branch=master)](https://travis-ci.org/Shopify/sarama)
 [![Coverage](https://codecov.io/gh/Shopify/sarama/branch/master/graph/badge.svg)](https://codecov.io/gh/Shopify/sarama)