use svg rather than png for godoc badge

README.md

@@ -1,6 +1,6 @@
 [![Join the chat at https://gitter.im/go-jira-cli/help](https://badges.gitter.im/go-jira-cli/help.svg)](https://gitter.im/go-jira-cli/help?utm_source=badge&utm_medium=badge&utm_content=badge)
 [![Build Status](https://travis-ci.org/Netflix-Skunkworks/go-jira.svg?branch=master)](https://travis-ci.org/Netflix-Skunkworks/go-jira)
-[![GoDoc](https://godoc.org/gopkg.in/Netflix-Skunkworks/go-jira.v1?status.png)](https://godoc.org/gopkg.in/Netflix-Skunkworks/go-jira.v1)
+[![GoDoc](https://godoc.org/gopkg.in/Netflix-Skunkworks/go-jira.v1?status.svg)](https://godoc.org/gopkg.in/Netflix-Skunkworks/go-jira.v1)
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)
 
 # go-jira