Update readme to refer to circle

Author: kpenfound

README.md

@@ -1,10 +1,10 @@
 # go-getter
 
-[![Build Status](http://img.shields.io/travis/hashicorp/go-getter.svg?style=flat-square)][travis]
+[![CircleCI](https://circleci.com/gh/hashicorp/go-getter/tree/master.svg?style=svg)][circleci]
 [![Build status](https://ci.appveyor.com/api/projects/status/ulq3qr43n62croyq/branch/master?svg=true)][appveyor]
 [![Go Documentation](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)][godocs]
 
-[travis]: http://travis-ci.org/hashicorp/go-getter
+[circleci]: https://circleci.com/gh/hashicorp/go-getter/tree/master
 [godocs]: http://godoc.org/github.com/hashicorp/go-getter
 [appveyor]: https://ci.appveyor.com/project/hashicorp/go-getter/branch/master