Update build badge

Author: marcuswestin

README.md

@@ -1,7 +1,7 @@
 WebViewJavascriptBridge
 =======================
 
-[![Build Status](https://travis-ci.org/marcuswestin/WebViewJavascriptBridge.svg)](https://travis-ci.org/marcuswestin/WebViewJavascriptBridge)
+[![Circle CI](https://img.shields.io/circleci/project/github/marcuswestin/WebViewJavascriptBridge.svg)](https://circleci.com/gh/marcuswestin/WebViewJavascriptBridge)
 
 An iOS/OSX bridge for sending messages between Obj-C and JavaScript in WKWebViews, UIWebViews & WebViews.